If you have the money for a DSTWO, which has lately been around 30-some dollars, then get it since it's worth the ~2.5x the cost of an AK2i. The addition of the CPU adds the ability for people with DSi/XLs to play GBA games and soon SNES games and possibly many other console games (SDK for Homebrew Developers is out now.)
Of course the GBA emulator is not 100% but it does play MOST titles. The standard compatibility is improved tremendously when using game_config.txt that was made for the gpSP emulator.
I don't expect the SNES emulator to be 100% either but I do expect it to be better than the current SNES emulation.