TPG special report: Best US airlines of 2021

What a difference a year makes.

Our 2020 best airlines report had a very different look than in years past. With the entire industry still in the grips of the coronavirus pandemic, we pivoted to highlight those carriers taking the most significant steps to keep passengers safe in the skies.

But today, it's a different story.

Travel has surged back, with domestic demand reaching pre-pandemic levels and the TSA now regularly screening over 2 million passengers a day. Here at TPG, we're thrilled by the travel recovery — and just as excited to return to a more traditional methodology for determining which U.S. airline offers the best overall experience for flyers.

Without any further ado — here's TPG's list of the top U.S. airlines in 2021.

Best US airlines of 2021

1. Delta Air Lines.
2. Southwest Airlines.
3. United Airlines.
4. Alaska Airlines.
5. American Airlines.
6. JetBlue Airways.
7. Hawaiian Airlines.
8. Spirit Airlines.
   
9. Frontier Airlines.
10. Allegiant Air.

Read on for more details on how the data led to this list.

Overall ranking and scores

For starters, here's a summary of the scores that led to the above rankings — including where they landed in 2020 along with where the airlines excelled as well as where they faltered in 2021 (see below for our full methodology).

Let's dive into each of these areas to see how the airlines finished where they did.

Best airlines for reliability

Whenever you book (and then take) a trip with a given airline, you want to know just how likely it is to go smoothly. This doesn't involve just the flight itself — it also involves the chance of having mishandled luggage or being bumped from your flight against your will.

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For the reliability portion of this report (which made up 30% of the overall score), we looked at five factors:

• Timeliness — How frequently a flight was delayed.
• Cancellations — How frequently a flight was canceled.
• Involuntary bumps — How frequently a traveler was involuntarily bumped from an oversold flight.
• Baggage — How frequently an airline mishandled a piece of luggage.
• Wheelchairs/scooters — How frequently an airline mishandled a mobility device.

Leading the way in the timeliness category was Hawaiian Airlines, with Southwest and United rounding out the top three. Of Hawaiian's flights that were not canceled, 94.4% of them arrived on time (defined as within 15 minutes of the scheduled arrival time). However, Spirit Airlines took the top spot for having the fewest cancellations — just 1.57% of its more than 116,000 flights did not take off.

Allegiant took the bottom spot in both these categories, with just 84.32% of its uncanceled flights arriving on time — and a whopping 12.63% of overall operations getting canceled.

The category for involuntary bumps ended in a three-way tie at the top, as Allegiant, Delta and Hawaiian had exactly zero involuntary denied boardings during the 12-month period. Frontier was the worst, with 3.6 passengers out of every 100,000 denied boarding.

Allegiant also was the top-performing airline for both checked baggage and mobility devices, as it mishandled only 1.33 bags out of every 1,000 that were checked and just 0.55 wheelchairs or scooters out of every 100. The worst airline for baggage was American, which lost 5.59 bags for every 1,000 checked — and Spirit was the worst at wheelchairs and scooters, mishandling 3.12 for every 100 of those devices that passengers checked.

Read more: What to do when your luggage is delayed or lost by an airline

Best airlines for travel experience

Getting you (and your belongings) to your final destination is just part of what you buy with an airline ticket. The actual travel experience is another critical element — which made up 25% of the overall scores above. Here are the factors that fell into this part of the analysis:

• Cabin features — What you'll experience on board, including Wi-Fi, seat pitch and width, and inflight entertainment.
• Lounges — How easy it is to find (and get into) domestic lounges.
• Family — How well the airline implements family-friendly policies for those traveling with kids.
• Customer satisfaction — How frequently customers complain to the U.S. Department of Transportation.

JetBlue scored the highest for cabin features, as it's the only airline that offers complimentary Wi-Fi and seatback television screens on every single one of its planes (no other carrier provides even one of those amenities fleetwide). Alaska and Delta took top marks for lounge access, while American came out on top in the family category — mainly for including all dependent children in its guest policy for Admirals Club lounges and for extending Main Cabin Extra seating and checked bag fee waivers to AAdvantage elite members' companions.

Related: Score free and discounted inflight Wi-Fi with these credit cards

Three airlines tied for the lowest marks in the cabin features section: Frontier, Allegiant and Spirit. These low-cost carriers offer more of a no-frills experience, not only in the a la carte service model but also in the hard product — think no Wi-Fi, no TVs, no outlets and comparatively cramped quarters.

Finally, the customer satisfaction data took on even greater importance in this year's analysis, especially the complaints in the early days of the pandemic. There was wide variation in how airlines offered refunds for canceled flights — prompting multiple rebukes from the DOT as some carriers did not initially comply with federal requirements.

And the complaint data lays bare which airlines were the best, and which ones left something to be desired.

Read more: Why you should wait to change or cancel your flight if you want your money back

Topping the list? Southwest Airlines, with an average of just 3.17 complaints per 100,000 passengers. The rest of the top five — Allegiant, American, Delta and Alaska — all had numbers below 10 complaints per 100,000 passengers.

And then there's the bottom three:

• United averaged 27.27 complaints per 100,000 passengers — not surprising at all, given the multiple changes the airline made to its schedule-change policies that greatly restricted customers' ability to obtain refunds (it finally relented after nearly three months).
• Frontier averaged 51.76 complaints per 100,000 passengers — and its numbers even increased from May to June 2020.
• Hawaiian averaged a whopping 103.61 complaints per 100,000 passengers — more than 32 times higher than Southwest. The Honolulu-based carrier also made several adjustments to its policies before finally backtracking in late June 2020.

It's worth noting that the complaint data by itself was nearly enough to drop Hawaiian into eighth place overall — as it edged out Spirit by just 13 hundredths of a point. Had the carrier experienced a "normal" year for consumer complaints with the DOT, that would've been a much healthier margin.

Best airlines for costs and reach

Another important consideration is just how easy it is to actually fly a given airline to your desired destination — and what it's going to cost to get you there. This made up 20% of the overall score, and was broken into three separate criteria:

• Route network — How many (domestic) airports an airline serves.
• Affordability — How far (in distance) you can fly for the money you're paying, based on financial data from the Bureau of Transportation Statistics.
• Bag/change fees — How much you'd need to pay in ancillary fees.

Not surprisingly, the three major legacy carriers scored highest in the route network criteria — which many airlines pared down during the worst of the pandemic, temporarily dropping dozens of destinations from their respective spring and summer schedules. United took the top spot, serving an average of 230 different domestic destinations each month over the 12-month period. It was followed closely by American (an average of 227) and then Delta (207). Hawaiian, meanwhile, took the bottom spot, averaging just 15 domestic cities per month.

Affordability is the area for low-cost carriers to shine — and that's exactly what they did. This measures how far you can fly for the money, and Spirit scored the highest here, clocking in at $86.60 per domestic revenue passenger mile. Frontier and Allegiant were close behind, at $105.51 and $110.75 per RPM, respectively. Delta, meanwhile, came in last — at a whopping $305.32 per RPM.

Translation? For every dollar you spend with Spirit, you can go farther — over three and a half times as far, in fact.

The final item in this section involves some of the most common ancillary fees that passengers face — those for checked bags and ticket changes (though the latter have largely been eliminated). There's a common winner here, even with the sudden updates to long-standing change fee policies: Southwest. The Texas-based carrier charged just $0.31 in these fees per passenger — compared to last-place finisher JetBlue, which averaged $12.40 per passenger.

Read more: How to avoid checked baggage fees on major domestic airlines

Best airlines for loyalty

The final part of the score is loyalty — obviously of major importance to us here at The Points Guy. This made up 25% of the analysis and consists of the following criteria:

• Frequent flyer — How rewarding a program's loyalty program is, including TPG's monthly valuations, elite status, cobranded credit cards and partners.
• Award availability — How extensive (and valuable) domestic award availability is across different time periods.

United took the top spot for frequent flyers, just edging out Delta in second and American in third. While the carrier did make multiple negative changes to its MileagePlus program during the pandemic, it nevertheless offers the largest number of partner airlines for both earning and redeeming miles, and United Premier elite status confers some notable benefits.

For award availability, Southwest rose to the top, as it offered the widest availability at the best value compared to other programs — the routes we analyzed saw an average redemption value of 1.43 cents per Rapid Rewards point.

The airline falling to the bottom of the rankings in both categories was Allegiant. The carrier offers some great value for those located in smaller, underserved markets — unfortunately, to earn miles in any way when flying Allegiant, you must be a holder of its cobranded credit card. This exclusion results in the low-cost carrier scoring near zero in the loyalty category.

Methodology

As noted above, there were four broad sections in this analysis, each of which consisted of multiple criteria. In order to focus on the airlines' operational performance wholly during the coronavirus pandemic, all data was based on flights operated during a 12-month period that ran from April 1, 2020, through March 31, 2021.

Here's a breakdown of the methodology and the data used for each:

• Reliability (30%).
• Timeliness (using data on delayed flights from the DOT).
• Cancellations (using data on canceled flights from the DOT).
• Involuntary bumps (using data on involuntary denied boardings from the DOT).
• Baggage (using data on mishandled baggage from the DOT).
• Wheelchairs/scooters (using data on mishandled baggage from the DOT).
• Experience (25%).
• Cabin features (using seat data from SeatGuru and inflight amenity offerings from each carrier's website).
• Lounges (using numerical data on the number of lounges, number of cities and price of membership for each applicable lounge network).
• Family (using a 0-to-5 score based on boarding, perks and food/entertainment on board).
• Customer satisfaction (using data on customer complaints from the DOT).
• Costs and reach (20%).
• Route network (using the monthly average of domestic cities served by each airline from the DOT).
• Affordability (using financial data from the BTS).
• Bag/change fees (using financial data from the BTS).
• Loyalty (25%).
• Frequent flyer (using data from our monthly valuations, elite status reports and each carrier's website).
• Award availability (using real-time award inventory for popular domestic routes across three distinct time periods).

For all criteria, the raw scores from the data were converted into a scaled score from 0 to 10 and then weighted using the above percentages to arrive at the final score. This ensured that relative differences among the airlines were accounted for in the computation.

In most cases, a score of 0 was assigned to the lowest-performing carrier. Where possible, a score of 10 was assigned to a "perfect" airline — for example, Allegiant, Delta and Hawaiian all scored a 10 on involuntary bumps, since they had zero IDBs during the 12-month period. However, when there was no clear way to determine perfection, a 10 was given to the highest-performing airline.

Final thoughts

For the third straight year, Delta Air Lines takes the top spot in TPG's special report on the best airlines in the U.S. The carrier wasn't a standout in any single category — it was fifth for mishandled baggage and fourth for customer complaints submitted to the DOT, for example.

However, Delta only hit the bottom spot in a single element (affordability), otherwise maintaining solid scores across the remaining data-backed criteria we analyzed. This consistency helped push it to the top spot.

Only time will tell if Delta can make it four times in a row next year (some early headaches don't bode well), but — for now — Delta is holding on to its title.