It was a combo of factors for me. Mostly Base, movement & contract.

Base: Commuting sucks & moving is expensive..

Movement: Personally, I would be willing to give up some contract & pay for movement, but not so much so that if the quick upgrade does not pan out that I will be stuck in a miserable place. Also, movement isn't just about upgrade time... How long is it going to take to hold a line? How quickly can you get far enough up the seniority list to have some buffer if the economy tanks and airlines furlough?

Contract: I wouldn't want to be at a regional with a bottom of the barrel contract. I feel there is a big difference from the top end of the spectrum to the bottom. The places in the middle have alright contracts and I was willing to give up a 'top contract' place in order to live in base and, hopefully, only be on reserve for a few months at the most.

Pay: First year pay seems to hover in the low 20's pretty much across the board, so not much of a differentiating factor.

Flow: seems nice if it actually happens. In general, it seems that flow-throughs have so much fine print that not that many pilots actually end up benefiting from them.

Equipment: IMHO, a jet is a jet.