Hugin's not a plugin. It's an application. It's cross-platform, so you can run it on a Mac, Windows, or Linux box.
AutopanoPro is Windows software and doesn't run on OSX, without some form of Windows emulation.
I'd recommend Kekus's Calico, which is an OSX port of
Autostitch. It's the same codebase that AutoPanoPro uses. Autostitch itself is open source and can be used on a Windows box for free, but both AutoPanoPro and Calico are commercial software.
Hugin may be harder to use, but it's far richer, feature wise, and far more flexible in the types of panoramas it can stitch. And it's open source, which means free as in free beer, and technologically it tends to be on the bleeding edge vs. other stitchers.
PTGui is a commercial piece of software that also runs off the PanoramaTools code base (which is what Hugin uses), and is the closest to a push-button solution for all types of panoramas (cubics, cylindrical, etc.) that I've seen. It's cross-platform (Mac/Windows, no Linux), and relatively expensive to the cylindrical-only Autostitch-based tools.