The Dreamcast has some great emulators.
It can emulate the Snes (DreamSnes) and Megadrive 'ok', some problems, but it's still well playable. The Megadrive emu is illegal though as it's a rip of the sega smash pack.
It can emulate the master system PERFECTLY, (SMEG)
not sure about the other 8 bit systems but I believe it can do those perfectly to.