Ive posted about the DS racers so many times...
Let me start off with Asphalt Urban GT 2.. IT SUCKS
first, it's only 30fps, so there goes the sense of speed, all you're left with is a sense of a choppy game, add the terrible physics, AI, collision, and you can't tell whats going on.
I don't know why people praise this game, it's garbage.
It may surprise you to know, I like the first Asphalt on DS, it was one of the first games I bought.
It's about the same as the sequel in regards to the physics, AI, and collision, but with the 60fps you can tell whats going on and it has a great sense of speed. Best arcade racer on DS.
I even bought both Need for Speed Underground 2 DS (terrible name) and Need for Speed Carbon.
NFSU2DS is a pretty unforgiving game, tough, but realistic physics, tough AI.
The game is challenging, half the courses you have to get absolutely perfect, as in never hit a wall, an oncoming car, and it pays to cause other cars to crash. It's an intense game and a lot of people wrote it off because it's hard, but it's good, they just suck at it.
Need for Speed Carbon is also pretty good, it's easier than Underground2, the physics are more arcadey, underground2 was borderline rally really..
I would recommend both of them, underground2 is hard if you want a challenge, one of the only racers I've ever played when you feel like you're going too fast and you need to slow down.
then of course mariokart, but anyone will recommend that