Southwest Airlines is probably the best carrier in the USA, full stop. I have heard good things about JetBlue but have never flown on them. Though it is considered a low-cost carrier it beats the pants off of the major American airlines. It is incredible how bad the major American airlines are. It is difficult for me to say that as my father retired as a pilot from United Airlines.
Let us begin with Southwest’s best perk, two free checked bags. All airlines now charge for checked bags on domestic flights, except for Southwest. Not just one checked bag, but two heavy checked bags. It is incredible. Fares are reasonable and they have sales often. Then there is their route network. It covers the country quite well and as long as you are just flying domestic there is no reason to fly any other airline. The employees are usually quite friendly and fun(especially in comparison to the ancient and bitter national carriers cabin crews). The seats are comfortable enough except when you have two whales sandwiching you in, as happened on my last flight, and actually happens quite often in the USA.
The only disagreeable thing I have found is the boarding process. It is a bit of a mess. But then again since people on all flights always crowd the jetway and ignore their boarding zone there really isn’t much of a difference. Their fleet is all Boeing 737’s which is a very old plane, but they take good care of them and are updating with the newer versions. It is true their pilots are young and aggressive but I have never had an uncomfortable or scary ride. Just fast taxiing and landings. So I truly have nothing bad to say about flying on Southwest.
My father hated them when he was flying but that was back in the golden age when there was a difference between major carriers and low-cost carriers. Now that they are on the same level of service I have no qualms about being a fan of this airline.