If you want games, use Boot Camp.
If you want office applications, VMware Fusion or Parallels is fine
If you want 3D Performance but don't want to reboot into Boot Camp, Parallels
If you want stability and don't care about performance, VMware Fusion
I personally use Parallels for a Windows install on my OSX for personal use. It has some applications that are Windows Only, such as Quicken and Chinese programs.
For work, I use VMware Fusion because my scanner has issues under Parallels. Sometimes it'll connect, sometimes it won't. Fusion doesn't have this issue.
As long as there's enough ram and both products aren't fighting over a single USB device or whatnot, you can run both at the same time.