Best for general play, best for debugging/hacking, best for internet play (this can get odd), best for playing with mods of games (some of the N64 gets odd), best for ease of use (some of the PS1 stuff has emulators that run most games well but others might run others better if you spend 5 minutes fiddling), best for extra filters (HD retextures and the like), most accurate (accuracy is nice and probably even one of the more important goals but it is not everything)....?
It sounds you just want to play games and would be happy if it has some cheats and the accuracy is in the "if you really know the system you might be able to tell that the audio decay is not as fast as it should but it otherwise it is all good" range but I have to ask. About the only real thing to note is with the rise of android and various handhelds/consoles some people pick certain things to make it easier to transition between systems.
