The newest one, EP-40, just came out! It's got the best specs by far and the features are a superset of the original EP-133, so it would be my strong recommendation. Unfortunately EP-1320 never received any updates so it lags behind, but hopefully they remedy that. Just don't buy hardware with hopes of unpromised future updates!
Edit: Because they don't make it totally clear- whichever one you buy, you can clear all the stock sounds and make any genre of music, regardless of the theming.
Edit: Because they don't make it totally clear- whichever one you buy, you can clear all the stock sounds and make any genre of music, regardless of the theming.