Based on some early testing, DraStic blows NDS4droid out of the water. The thing is it has to be sideloaded, but it reads input from the Ouya controller so you can map the controls to the controller! Read more for some other notes.
Under configure options
-Check Mult-threaded 3D rendering
-Under input, check a “no mapping box” then click Map keys
-Disable mapped keys in overlay (removes on screen controls)
-Check Savestate overwrite needs confirmation
-I recommend playing games that primarily rely on controls, rather than touch
-To find bios files, search in google (be sure to save them to Download folder of Ouya)