I don't know about the seniority and odds of getting bases with Shuttle, but here's the way I look at it all. Throw your application their way, twice if you have to, and see if they'll interview you. They won't guarantee you a base because they can't. They will guarantee you a certificate though. There may be some shuttle guys who could shed some light on the odds of you getting ORD for a base as a new hire.
As for the above post...the whole reason GoJet was created was because it was cheaper in the first place. This is why I would GUESS that they have a base there and not TSA. Among other reasons probably...