But I would say that the best sounding 303 style groovebox is Audiod. It has a sharpness to its sound that cuts through in a good way that is missing from other Android 303's.
When it first came out it was pretty useless as it had some problems but with some updates it is a hidden secret. It has some deep sound shaping functions in one of the sound engines then the 303 plus two drum machines. It also sports one sequencer that works in its own special way etc.
I have written about it before but seeing this video felt the need to mention it again.
It works better on tablet as the it can become a little bit fiddly on a smaller screen. (With fiddly interfaces and small screens I suggest getting a pen...)
Anyway enjoy the video.