The NDS definitely has the best library of games to choose from. There's a solid wall of games to play that would satisfy anyone's tastes. Thanks for the link, Spinosaurus, I haven't heard of half of those games but I'm really interested in playing them all.
As much as the DS might be "dead" considering the 3DS exists, it's still very much alive to me. I have dozens of games laying around that I haven't started playing due to the giant roster of games that I'm currently going through.