I started with Parallels and then when it was time to upgrade I went with the VMWare Fusion crossgrade (which was the same price as Parallel was asking for the upgrade to their newest version).
Both work surprisingly well but Fusion has been more stable and a bit quicker than Parallels was. But as I’ve never used the latest version of Parallel I can’t say how it compares now.
I think either will work well enough to do the job. Windows viruses aren’t going to be a problem unless you set it up to have your Mac drive fully accessable to the Virtual machine running windows. I don’t think its really the place of a piece of software like Fusion or Prallels to protect you from Windows Viruses. They are both essentially platform agnostic as it is. (They aren’t just for windows, you can create Linux virtual machines and so forth). If you are really concerned there is nothing stopping you from installing virus software in the Windows install.
Jamie