PF auto crops the stitched panorama, AS doesn't and leaves you to decide how to do it.
Having used both I was very impressed with the results of PF but the lack of auto stitching (and until recently the lack of multi row support) frustrated me - manually stitching 37 photographs is a pain...
However, the major problem for me was PFs inability to stitch 2 images together of different resolutions
In the end it's a personal choice