I have to say I'm impressed with Photoshop CS (photomerge command). Works well with telephoto (and obviously telescope) shots due to the long FL so everything is usually nice and square.
I have no experience with photo stitch (unless that's the one that Canon distribute with their cameras... in which case I have

).
I do a lot of panoramic stuff and have used some different programs over the years. Arcsoft Panorama Maker is very good as long as images are in a row... it gets tedious fudging it to handle 2 dimensional arrays of photos. It handles wide angle images well provided they aren't hand held, but doesn't cope with conical distortion (camera pointed up or down from the axis of rotation).
Another program I used years ago that might be worth a look is Panavue. The trial version puts nasty little logos over your image, but from memory it handles conical distortion, 2 dimensional arrays and hand holding errors very well.
Al.