I have Jarcade, Cps2hd, Android Arcade and TigerArcade on my Droid.
Android Arcade = completely worthless, don't bother.
Cps2hd = only support cps2 games but play them perfectly.
Jarcade = great for cps1 games and neogeo, support most of them from the 90s era...... main problem is you need mame 0.34 set wich is very hard to find, support also more oldschool games like Pacman, Dig Dug, etc.
TigerArcade = it sucked at first but with the new version 1.2, wow! this is the best arcade emulator so far.... it runs all cps2 games perfectly... all cps1 games (with sound problem), all neogeo games perfectly, all Cave games from the 90s but with sound problems, and most Toaplan games also work. Plus its FREE unlike all the 3 other arcade emu.