I have a 15" Bailey, on a Little Gracie II. I'm very happy with it.
amandasgramma, what is the throat space on your Pfaff? If it's 9" or less, then that's technically a short-arm (I know some places that sell them like to call a 9" a mid-arm, but it really isn't, IMHO). I personally wouldn't consider something a mid-arm unless it was 13"/15" or bigger. On my 15", I can easily get 12" when I first start quilting, and even when I get towards the end of a large quilt, I'm still getting at least 8" or so of space.