Either m3i zero or Acekard2i would work, pick what is right for you. Make sure to use AKAIO for the AK2i.
Acekard2i:
Pros:
AKAIO FTW!!!!!!!
BootFlash upgradable through dsi 1.3 and below, DS or DS LITE
Best compatibility, with AKAIO
Reliable and easy to use
Good spring loaded micro SD slot(although this could fall into PROS and CONS.)
Able to update loaders and cheats via wi-fi
Fast Updates for it
Cons:
Only able to be bootflash upgradable through DSI 1.3 and below,DS and DSLite
No RTG or RTS
M3I Zero
PROS:
SAKURA FTW!!
RTS feature
RTG feature
Able to be updated without a DS or DSI 1.3 and below
CONS:
Bad card build
Fairly slow updates, as of now
The USB update cable seems fragile and could snap
Bad homebrew compatibility
SO pick whichever is good for you, Make sure to Buy it from www.gamebygame.com, free shipping for US customers and fairly low prices. Also almost forgot to mention, they check each flashcard to verify it working, so you don't have to worry about the card failing on you.