Seeing as you’re posting this on the AA side, I have a feeling your mind is made, but I’ll write this anyway.

Just a comparison for you:
9 flights/day to DFW from BNA all AA, or 10/day to ATL, 7 of them being DL and 3 WN.
You can reserve jumpseats at DL, too, with priority being given to first going to work, then coming from work, then personal travel (priority being how far in advance you can list).

However, I drive ~3 hours to my Delta base and although that would probably be my limit, having the choice and control of driving makes this job a game changer.

I’ve really enjoyed my time at DL and upgrades are still going junior (less than 10 months for 717 and 220, others shortly after that). You’re on the backside of the wave, but you’re young. You’ll retire relatively senior regardless, and that retirement wave only matters if the company continues to hire behind you. Oh, and the 18 hour callout is a hell of a thing.