Which game should I get?

[:DSman]

I'm having a hard time deciding which game I should get:

 

Mario Kart DS or Pokemon Platinum. I have Mario Kart Wii already and I also already have Pokemon Pearl. I'm not sure which to choose but the one I do choose will be picked up on Apr. 5th when I get my new Nintendo DSi

 

Or it would helpful if you could reccomend a completely different game. Thanks in advanced :D