I know quite a few guys at JetBlue and here at Spirit. None I know have apps in at the other. A solid half of each have apps in at DL/UA/AA. If that small sample group is any indication, one isn't substantially better than the other.
As far as bases go, I get the appeal of being based where you live. If your heart is set on NE I'd look favorably at JetBlue. Most everywhere else would be Spirit. FL I guess would be 50/50. This is, of course, the airline industry, so bases will come and go. Bases close/shrink at the biggest airlines (DL/CAL/etc) and the smallest (Spirit has had more bases than I can remember). Also, the OP mention LGB. Moving there is great, but if your concern is upgrade, you could be limiting yourself. Just like DTW at NK .
Money/contract:
The contract is what it is. Keep in mind that Spirit got this contract in 2010, and at the time it was much more competitive. Think of what our counterparts at US Airways, United, and Virgin where making back then. I'm glad these airlines have all raised the bar since, and I hope that makes our lives easier on the next one. Our pay, benefits, and work rules are subject to change every 5 years, and today's low company could be tomorrow's high. Southwest in the late 90's vs mid 2000's is a great example.
I like some things in JetBlues working agreement that I hope we get, but for the most part I greatly enjoy the contract here. It's a work hard, play hard type mentality for me. As an FO in the top 50% I can bid conflicts every month or two. That gives me the option of having 20 days off for line value or working a little extra and bringing home some significant credit. Having the option is nice. I just got back from a camping trip (due to my conflict induced 8 days off) with a good friend from US Airways. Their Airbus compensation might be better than ours (only as of, what, a year ago?), but otherwise I prefer just about everything in our contract vs. theirs.
All just food for thought. Go where you get hired first, unless your heart is really set on something else, in which case keep trying and hope for the best. You can always leave for DL later!!!