Skywiz,
Very reasonable question. You've gotten lots of responses, some emotional, some filled with more facts than emotions. Good luck sorting out the gems from the hot air.
Others have said similar things. List the 5 things you want most in your airline career; money, variety of airplanes to fly, far/near international flying or mostly domestic, job security, labor/management work relationships, quickest upgrade, etc.
Once you have done that, assess the carriers that best match those goals and apply; I would apply to both. BTW, I suspect when the applicant window opens up again for SWA, it may initially be for "typed" pilots only. No official word but just a gut feeling, but if not, apply to both is my recommendation.
One example of how choices may not always work out the way you want them. Recently flew with a DAL '97 hire who came to SWA in the mid-90's (pre bankruptcy). Great guy, great attitude, super flying skills. Drove to work @ DAL, great QOL but concerned about bankruptcy and DAL's future.
Left DAL, came here and is not upgrading as quickly as he thought he would....when he came to SWA, the trend was all towards quicker upgrades at SWA. Bottom line, he'd be a CA at DAL now, would still be driving to work vs. commuting to work, has lost many thousands of dollars by not collecting post bankruptcy payouts to pilots, equity from bankruptcy as well as a CA upgrade pay. I don't believe he was ever furloughed but had concerns about it obviously.
He acknowledges the choice has cost him great sums of $$ but despite that he is very capable, has the "luv" spirit and isn't bitter at all. In hindsight he says he should've stayed but is living with the decision.
DAL on the surface as do other carriers appear to have better upgrades coming in the future. The same was said when I was hired in the late 90's...as well as bigger salaries for the legacies. The big difference is growth will come from retirements not from airline growth as it was "promised" in the late 90's or early '00's.
I luv SWA and feel fortunate to be here, wouldn't want to be anywhere else but it isn't the right fit or choice for everyone, I get that and respect it.
One can have very successful airline carriers at other carriers; timing, leadership at the top and a world of unknown variables that can change a company's future in the blink of an eye will be more of the determining factors of your "success or missed opportunities" in this world we call the airline profession.
Once you choose the top 5 things that are most important to you in your career, go back every year or so and review them and make sure they stay the same; if you become unhappy at your airline it is probably because those priorities have changed or you weren't honest with yourself to begin with. Good luck in your choices.