DSTWO. Still receives updates from its creation team when games or DS/3DS systems require it, will work with a DSi or 3DS if you ever decide to upgrade, and it will essentially do anything any other flashcard will do and more (it has its own CPU and hardware built in to support superior SNES emulation over that of the normal ones on other cards).
Though as Rydian said, get a slot 2 expansion card such as the EZ Flash 3-in-1 for GBA games on a DS Lite. The DSTWO does have a GBA emulator of its own, but it's nowhere near as good as playing GBA games on a slot 2 card. The compatibility and speed isn't anywhere near as good. The slot 2 runs them natively as they would play if it were a real GBA cartridge.