It's all subjective, but here's my thoughts:
I've used Fusion since 2.0 and have rarely, if ever, had a problem with it. From my own experience, I seem to see more complaints/issues with Parallels. They're definitely on the bleeding edge, but frankly, I just want something that allows me to get into Visual Studio easily and reliably.
Also, the last time I paid for Fusion was 3.0, about this time 2 years ago. Contrast with Parallels who seem to put out new major versions much more frequently, and the cost of ownership in the long run makes a significant difference IMO.
Usual advice; try both, but my recommendation is Fusion.