My two cents:
I've been very happy with PT Gui. Yes, it takes a while to learn, but John Houghton's excellent tutorials are a great help.
http://www.johnhpanos.com/tuts.htmI tried Autopano (not Autopano Giga) a few years ago, and it worked well but, for my system at least, the processing times were at least five times longer than PT Gui's. Also, although Autopano has some nice features, like automatically finding the "stitchable" pictures in a given folder, I didn't feel they were all that useful. Once the novelty wore off, I found plain old dragging and dropping into PT Gui worked just fine. Maybe I'd have liked Autopano better if I'd stuck with it longer, but I didn't have the patience to figure out two programs with very dissimilar controls.
As has been noted already, if you're only creating landscape scale panoramics, almost anything will do the job. That applies to software, and hardware, too. If nothing's close to the camera, parallax isn't an issue, so you're free to hand-hold and process with Photoshop, Panorama Factory, whatever you like. It's when you start shooting indoors and into the spherical world that everything gets much more interesting (read: painful, expensive, frustrating, but rewarding). Then you need a dedicated piece of software to accompany your specialist panoramic tripod head. Again, PT Gui is my choice. (And Nodal Ninja gets my vote for pano head.)
If you
are shooting hand-held panoramics, here's an unsolicited suggestion: When you run into a setting which includes some foreground element (historical marker, phone pole, your spouse), try to fit the whole object into one shot of the sequence, even if that means going back and taking an extra frame. Then mask out or otherwise eliminate that object wherever it appears in other frames. This technique eliminates the parallax between near and far elements because they both now live in a single frame.
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