i would try and emulate a sega system. i wuldnt bother with trying to emulate x box or gamecube for ages, coz most ppl's pc's wouldnt be able to handle it. and considering most n64 titles run far from perfect on emulators i think it would be a bad idea to emulate such advanced consoles.
i would really like to see a perfect saturn emulator for all those sega classics, or if you wanna be ambitious, a dreamcast emulator.