VMWare offers better performance than Virtual PC in every category. (Click to see full results from ArsTechnica)
I'm in the middle of doing a technical performance study of VMWare, so this ARS Technica comparison of VMWare and Virtual PC
was interesting to me. This review is primarily concerned with single user copies, not the beefier "server" versions. If you're a developer who needs to run lots of different OS's, this is a great solution. Development groups with this need would do well to buy a copy of virtualization software for each engineer and then create a library of images that they can use as needed. I have a few friends who do this and swear by it. All things considered, if you need anything but Windows virtualization, VMWare is probably the better choice since Virtual PC (a Microsoft product) does not officially support running Linux and there appear to be some issues. On top of that, VMWare offers better performance, according to the article, in every category over Virtual PC.