Nuuuu! Don't make me choose between mah baybeeez! *sigh* Well if I had to rank them it would go like this:
1.Sonic (nostalgia points!)
2.Zelda (More nostalgia)
3.Pokemon (Nostalgia! I'm sensing a trend here)
4. Mario (Mario was my first DS game *sniff*)

**Please note that all of these where in a close (and I mean CLOSE) tie! And they are pretty high up on my top favorite games list!