This is subjective, perhaps. I’ve always used Fusion. It’s worked great. I’ve heard a lot of hype about Parallels (7) so decided to try building my Windows 8 Server VM on it (supported in latest builds). This was a disaster. Hung repeatedly, the start bar kept “flicking” as if explorer was crashing and reloading really fast. Explorer did crash a bunch of times. Mouse capture was unreliable. I tried a few solutions listed in the Parallels KB to no avail.
I’ve just rebuilt the same VM on Fusion Technical Preview 2012, also offering Windows 8 support and the experience has been the same as that of my previous 2008 R2 VM, ie flawless.
Now you know.