Dstwo, or a R4i Gold by the R4ids.cn team
they both have the top compatibility with games, dstwo has more features but it costs abit more
the problem with card is not there gaming ability, the way to judge the best is the Firmware Updates provided
DSTwo, is always the fastest to receive updates, R4i Gold by the R4ids.cn shortly follows after it
Firmware is what has to be updated to work on a new 3DS update, so the card must be updated before the console,
Kernel is what needs updating for newer games to work, the DSTwo does normally not even need and update, all other cards always do