clipped from: www.tuaw.com   
Like it or not, lots of us who own Intel-based Macs have to run Windows from time to time. Although Boot Camp is pretty fantastic if you need to run a processor intensive application (or you want to play games), virtualization is the more attractive solution for users who need to access productivity applications

The two big players in the virtualization field are VMWare's Fusion and Parallels' Parallels.

Parallels came out ahead in many of MacTech's tests. For certain more processor heavy uses, VMWare, thanks to its ability to take advantage of both cores, came out the best.