If you want high NDS and Homebrew support with okay GBA support then I recommend:

Supercard Lite
Passcard 3
Taiwan 1GB Kingston Micro SD

Allot of people will tell you that the GBA support on Supercard is low but all the games I have tried work fine except Metroid Fusion which runs slow in sprite heavy places. Still very playable though and actually makes the game easier

Of course if you are facing slow down problems in a GBA game then you can try the multiple speed up methods with the restart patch and QCP saving method which you can read all about here: http://wiki.pocketheaven.com/SupercardGBASlowdowns

Also you will hear people talk about NDS games running slow and crashing allot and this is especially the case with the 2 DS Castlevania games. Allot of people think its to do with what Micro SD card you use and using the one I recommended above (Taiwan 1GB Kingston Micro SD) I had no problems in most games. Games like: Mario Kart, Metroid Prime Hunters, both Castlevania games, Resident Evil DS, Final Fantasy III, Advance Wars DS etc. All ran perfectly fine with the latest firmware and patcher from Supercard.cn

Cheapest place I know of online to get the Supercard Lite and Passcard 3 is http://www.gameyeeeah.com/. To get the Taiwan 1GB Kingston Micro SD card go on ebay, I did and picked one up for the cheapo price of £13 :thumbup: