My advice--
Research, Research and more Research.
Look at the competitive landscape and figure out if one is more likely to meet or exceed their growth plans. Look at the revenue stream and likelihood of serious cost issues coming up in the future. Is there a need for a pilot pay cut on the horizon? Does the company want or need to increase productivity? How are management labor relations?
Hedge your bets with a scenario where each makes a mistake or two and how well they can weather it. SWA, for example, has much room for error due to their strong balance sheet. Factor in competitors and their ability to put a squeeze on revenue. Stock analysts and airline forecasters can help but I look at their guesses with a jaundiced eye. I am concerned by CALs debt but their revenue looks good.
SWA is a really good company to work for. It is fun to go to work. I don't think management is out to bilk the company at SWA. That is really important to me. There is no substitute for a trustworthy management team.
What I would not use to make a decision, unless you have no choice, is first year pay. If that really is a factor I would focus on how to make low first year pay work if that company is worth working for.
The highest lifetime earnings is also on my list of what not to look for. I know I don't need to fly international. My goal is narrow body captain.
Schedule is a double edged sword. If you pick one because they are not flying 7 legs a day you have to ask if that is smart. If your productivity is lower at CAL, should your pay be as high? I think that is one reason why ATA guys are getting stuck with low pay right now. Its hard to make them productive with their route structure. For a cargo carrier low productivity is no problem but it is essential in the pax industry. SWA has no problem, IMHO, making pilots productive. This productivity allows higher pay with a smaller dent in the CASM.
Lastly, as others have said, many have played the forecaster game and made the wrong call. Its hard to predict the future. The further out your forecast the less accuracy you will have. I trust a 2-3 year projection oodles more than a 6-10 year projection.
SWA is a great bet, unless JetBlue and Airtran start beating them up. CAL is a great legacy bet, unless legacy mergers make strong rivals.
Finally, pray about it and be happy with your decision. But don't throw away your interview suit.