You're going to get flamed for this, there are tons of these threads already.
The R4 isn't worth buying anymore.
The Best Cards, expensive:
Acekard R.P.G, CycloDS Evolution
The Best card, mid range:
Supercard DSONE
Budget good cards:
Acekard2, DSToptoy/ToptoyDS
If you have any more questions, I guarantee they've already been answered, there's 100s of these threads already - I'm sure you'll be able to find them.