Would you like to have a emulator that has great debugging features, or just for fun to play games on? Because I highly recommend Regen for debugging purposes, while it's sort of unstable it's currently the only Mega Drive emulator that supports debugging features. However if you're wanting a emulator just to play games and possibly make videos, I suggest Kega Fusion as well. These two are very accurate emulators that are very close to actual hardware. If you're a Sonic fan, be careful with what hacks you play as some of them might not work on either emulator. (The main cause could be the hacker writing code to odd addresses...) However since i'm new I can't provide a link for either one, but Emulator Zone has these two emulators on the main downloading site.