I haven't read through all the posts, but I'll put my plug in (sort of) for American Airlines, but I'll caveat that by saying I live outside Philly, and at PHL, AA is pretty much the name of the game. During COVID, all three of the big legacy carriers basically made it so you can achieve status with credit card spend alone. So, I have every AA credit card there is - earned lots of sign-up bonuses - I use their SimplyMiles offers, their shopping portal, even did some of the Miles for Opinions surveys for miles, have booked some hotels through their hotel site, when I rent cars, I use
Avis because you can earn bonus AA miles. I've been Executive Platinum (their highest status outside Concierge Key which is by invite only) going on two years in a row. I believe Delta and United have similar ways to rack up miles - if I lived near one of their hubs, I'd probably look into their miles ecosystems.
So, I earn lots and lots of miles. The absolute best thing about having so many miles, is that when you go to book your flights, you have a TON of flexibility. You can cancel and rebook any time the miles redemption goes down. You can cancel and have your miles reinstated up until the plane takes off. On our most recent trip to MCO, I booked two different flights for our flight down - one on Friday night, one on Saturday afternoon - that way, if my Friday flight got cancelled (not unusual in the middle of summer for the last flight of the day if thunderstorms have kicked up on the East Coast), I'd already have a back-up flight the next day. Once my flight took off on Friday night, I canceled our Saturday flight and miles were immediately reinstated.
And, when you're using miles to book flights, it doesn't really feel like you're paying cash. Of course, I gave up the cash back I could have earned (and if I were diligent and set all that cash back in a savings account, I'd probably come out ahead that way). But, I enjoy playing the game to earn miles and get status.
Most of the perks that go with airline status these days are not worth it because so many people achieve status with credit card spend. But, if you're willing to put in some work, I think it can create a much more enjoyable experience booking and flying - I mean, you're still flying U.S. airlines, and none of them offer that great of a domestic service compared to airlines outside the U.S. - but, it is slightly better when you have status.