Mariokart wii or supermariobros. wii?

Both. And then again they are different kinds of games so you can't really compare them. In fact, I think that they both are better than the DS equivalent titles.
What do you want to do with this, buying one of them?
I have both, I like them both, but if you'd like to choose, think about what gerne you'd prefer: Racing or 2D platformer?
Also, think about the question: Do you want to play online? Or: Are you online for most of the time?
New Super Mario Bros Wii is my favorite Mario, so I pick that one! Super Mario 3 was 1st for forever but then this one took over! Mario Kart Wii is great too. But they are totally different games!
Who can compare two totally different games? I can't. But I like Mario Kart Wii more because I love making the computer's lives miserable and Wario.