SWA but keep applying to Delta and United, then jump ship if/when you get hired where you really want to be.

SWA is still great for flexibility and there are a lot worse things than being a senior guppy switch monkey while waiting for upgrade, but you're right to be worried about the MAX and how tightly SWA has tied it's future to a product that simply cannot be delivered by a company that's been on the fail train for years.