Drastic is the best emulator for Android. I have tested the Drastic demo and nds4droid and Drastic is way better optimized and has much better graphic options, you can run much smoother on your phone (I tested both on a Asus Zenfone 5). But would be cool to see a Desmume in the phones, it's the best emulator for PC I've used so far.

edit: Open NDS Emulator and Pretendo NDS Emulator are just forks of nds4droid, since it's the original open source project.