Since I'm not in an environment where those things count, but rather a consumer-centric world, I vote for Parallels. They have the edge on graphics performance and have pushed the idea of integrating other operating systems with the consumer's desktop very far in a very short time. If it hadn't been for Parallels Desktop on the Mac, VMware would probably still be much like VirtualBox a couple of versions ago: A(n almost) non-connected sandbox that feels very, very technical.
On the _other_ hand: Whenever I replace my main Mac computer, I end up installing Parallels and Windows, only to find that the main task I use it for is to keep Windows within it up to date and safe. I personally simply don't have that much of an incentive to actually have Windows running. All the things I really work on can be done better on the Mac. Checking what a site looks like on IE/Windows has become more and more irrelevant.