I've been using Parallels to run a linux vm, a test win7 vm and to fire up my bootcamped win7 instance nicely.
My only issue is that I'm using a previous version and parallels tools don't seem to install on the newer versions of the linux distro I need to use.
I believe one way to get them working is to upgrade (my linux skills are low so no idea if it's possible to get them running another way), which could turn out to be a yearly cost every time the distro has a major update.
No idea if Fusion has these issues, if not I may switch.
I will say that so far Parallels has been able to create a VM from pretty much anything I've thrown at it format wise which has been good.