It's pretty simple...
If consumer reports had to do one of their useful graphs on "FO Allegiant" vs "FO Spirit" without too much consideration for the medium to long term future (because that's all way too unpredictable no matter where you go) and with the consideration that you will live in a base... I think Allegiant wins "overall score" hands down. I think most would probably agree.
In the present day, Allegiant is a better place to be than Spirit (if you live in base). CP has told me that we have applicants who are currently at Spirit and Frontier (take that with a grain of salt of course).
my 2 cents
-Alex-