Older cards will not work. The newest R4 cards will work, at least until a FW update blocks it.
R4 is constantly getting blocked on 3DS(2DS) and having to change hardware to get past the block. The first R4 I got ended up being blocked with in 3 months. I do have a newer one that works though too. It is difficult to tell them apart or which version you have.
Supercard DStwo is more expensive but has more features and never gets blocked. It has better hardware so they usually issue a patch with in a day or so if a new firmware blocks it.