They are roughly equal, but XJT has better workrules I think. That might change over time since XJT is being integrated into ASA.

As you mentioned, if AE gets spun off that could create long-term instability, but any such sale would have to include a certain length of guaranteed contract or no sane buyer would touch it. If you just want to upgrade, get your time, and move I would guess you would have time to do that before the wheels come off. AE upgrades have been ten years in the past, but they appear to be more in line with other regionals now.

If you're looking for a regional career, XJT/ASA is probably a better bet although there are certainly no guarantees.

If you're looking to get your time and move on, I would pick the one which has base(s) near where you want to live.