I tried two NDS4Droid and DraStic. NDS4Droid worked OK but was rather slow, even on my S4.
DraStic on the other hand, is superb and has performed faultlessly. I strongly recommend it and I played Pokemon White (of which I have a legal copy I should point out) all the way through with no problems. It worked just as well as on my DS except for having on screen controls.
All the usual caveats about downloading pirated ROMs apply blah blah.