Looking for the best Emulator for all game systems

So I have a small form factor PC hooked up to my tv in my living room and want to install some emulators on it to play some old games. Can anyone recommend a Win7 emulator than can do multiple systems with a somewhat decent GUI? This pc should be powerful enough for ps2/saturns/n64 games I think, but the usual snes/nes/gameboys and more recent mame games should be good too. I like street fighter.