As for me:

Xbox
- better graphic than PS3(IMHO, don't flame me ok)
- steady online play (reasonable monthly fee la)
- I prefer Xbox controller than PS3, more solid and hand feel

PS3
- meant for exclusive title only
- like PSN games

Wii
- for entertain kids and wife Sexercise only

PC
- surfing and torrenting
- Diablo3 and emulator games

Personally I prefer to play games with console system, because you won't get virus from it. Ya, PC need expensive investment if you tend to last for few years and have high risk of getting virus and lost all your precious game data.