Visual Boy Advance may be the best Gameboy Advance emulator in our opinion but for the Nintendo DS we have to go with NO$GBA. Most of the Nintendo DS emulators are in early stages and out of those this is your best bet.

A very close second to NO$GBA and was also the first Nintendo DS emulator able to run some commercial games at a playable level. Its worth the mention becuase some games may work on NO$GBA and some may work on DeSmuME. Both good emulators for what can currently be done.