I use RetroArch for RA. You don't need their emulators unless you're authoring. You do need specific cores though. If you wanna know what cores to use, here are my suggestions:
FCEumm for NES (Rumor is QuickNES also works, but not for Android which is where I mostly play)
PicoDrive for SMS, GG, GEN, SCD
Beetle PCE Fast for PCE
Mupen for 64 (I think, not 100% sure)
SNES9x 2010 for SNES
Let me know if you have questions but the setup is pretty easy.