Mine is perfectly fine.
I'd say go with whatever's cheapest. I hear R4, M3, and CycloDS are the best three to choose from.
I acutally use mine to read eBooks, play GBA, GB/C, Genesis, and original NES games on the go, as well as various homebrew apps that I find scattered on the intarwebz. I think you can even find complete OS's around. I know they have DS Linux, etc, but those suck.
Oh yeah, and you can run DS games on it, but who does that?
<_<
>_>