I've been a VMWare Fusion user for the last year or so and it has run Vista on my macbook pro quite well. However, last week, I decided to give the new version of Parallels a shot. I'm loving it. Granted, I've "downgraded" to XP for the Parallels machine, but it runs like it is native. I couldn't be happier with it to fun the few apps that I just can't live without.
On a side note, I would recommend that you install your windows OS through bootcamp, then use Parallels or VMWare to run your bootcamp partition. This way, if you need to run windows natively, you have that option. You can't go the other way.
Both are great apps, Parallels gets the nod from me!