You might want to sit tight until next spring and see who's still standing after the merger settles out. If you want to jump now, Mesaba would be the best bet (just another pilot's opinion) with Compass a close second.

With today's trends, it looks like some of the NWA/Delta feeders will not get you any 121 jet PIC for many years (like 2016, if ever) so don't rush to place your wager. Err, I mean don't rush to pick your next regional.