funny how this question is asked but there are just 1 or 2 emulators for each console and some of them are an upgrade version with a diferent name
gbc\gb gameyob (there is lameboy, which is diferent, but its outdated, gameyob is better)
the others, i didnt tried them much
i know the gba and snes ones only work under a DSTWO (there is a gba emulator for r4 cards but its bad..)
nesDS is pretty neat for NES games