My understanding is that the most recent/significant growth has been on the RW certificate due to the Frontier operations. PIT seems to be in jeopardy of some downsizing due to the USAir pullout. I don't work there, so I don't know anything first hand.

You can upgrade across certificates so if it were me I would base it on where I wanted to live. As far as which would result in less time on reserve, I have no idea.