DAL is ramping up hiring big time, they're supposedly shooting for 70/week in indoc starting next year (i'll believe it when I see it). I assume UAL is doing the same, so that's probably a crapshoot either way. Both are great companies, but UAL has a huge edge on WB flying (if you're looking for that) as you'll get there much earlier with the sheer number of WBs and the fact they use 3 FOs on their long haul stuff. I'd ask your bros about reserve life at their respective carriers. As an in base guy (DAL), I'm a reserve bidder by choice and it's pretty dang good, especially when I was on the WB. For me, it's a coin flip between UAL and DAL....maybe the first indoc date solves that. SWA is last for me simply because of the lack of WB flying.
Congrats and best of luck! You really can't go wrong.