i would go to SWA....it has a great track record of success.
i was recently hired by JBLU, and i knew it would be a difficult decision to make whether to go or stay at the legacy where i am currently employed. i like the bases a JBLU, i would not have to commute unless i upgraded, great employees and good worker/ mgt relationship.
i decided to stay where i'm at. with JBLU loosing money, they are now in the same boat as most airlines, so i did not want to get stuck on the bottom of the list if they curtailed their growth plans.
at my current airline, half the list will retire in 10 yrs, at JBLU, i would gain relative seniority only if they continue hiring, since there are few retirements.
like i said it was a difficult decision, but for the time being my company is growing nicely, but not at the same pace as JBLU.