Well, in a perfect world, and in my opinion real 7.1 is the best.
I use a fully featured 5.1 reciever with my computer. When I listen to music I use stereo (mode) 2.1.
When I game I tend to use virtual surround. I would love to use REAL surround but from a PC game to a receiver you've gotta have Dolby Live or something else to re-encode the game audio into something the receiver can actually decode as 5.1. (This is only an issue if you use 1 cable for your surround sound.) If you don't then you'll need separate inputs for each set of the 5.1 speakers. My receiver has that while many others don't. I still use fiber instead because when I connect each one of the outputs from my PC to my reciever I get a lot of noise interference.
(I do plan to buy a Dolby Live capable USB external sound card for this reason.)
But ya, GTA Vice City in 5.1 while connected to my Playstation 3 (at the time) was pretty cool.