Actually, my preferred Genesis/Mega Drive emulator is
the version of Genesis Plus hosted on Michu's Emupage under the "XScale" link under "GenesisPlus".
It has both Cyclone and Musashi cores, has flawless Z80 emulation(PicoDrive and the OP's Genesis Plus link suffer from slowdown while playing Streets of Rage 1 and 2 with Z80 emulation enabled), and has virtual buttons both along the bottom bar and invisible ones along the right edge when oriented with the D-Pad on the left. I don't have any major problems with it, though I have to exit the emulator and restart it just to play a different game.