/title.
I think the most evil virus would be one where it stops the user from being able to do anything, including attempting to perform a hard reset, and then promptly attempting to force the physical components of the system to destroy themselves any way they can (ex. spinning up the fans to such a high speed they break, forcing the HDD to scratch itself, etc.)
The second most evil one would probably be one that deletes the OS and simultaneously corrupts the BIOS, A la CIH.