I prefer VMware, its easier to use and I found that running XP was faster in VMware than paralells. Plus version 2 of fusion has a lot of new features which are very nice, such as dual screen support.
I have both too. Personally I like VMware much better. I think that it's way less buggy than Parallels.
However as somebody already suggested, why don't you download both products and their two week free trial period and personally see which product that YOU like the most.