Trace Memory was really good, and so were the Mario & Luigi games... I'm having trouble coming up with a favourite.
I my DS when I was 10, (Yeesh, nine years ago?) and after that I went through games like most people go through theatre popcorn. It wasn't that fast at first of course, but once the games started hitting bargain shelves, I probably had a new game once every two weeks or so.
As you can imagine, I have a lot of DS games, but no one stands out as a favourite. I love many of them, and there are a lot of good memories tied up in those old machines, but I don't think I could choose a favourite among them.
I guess I'll try to pick a "Personal Best", which I guess would be Shantae: Risky's Revenge.
...But then again there's Cave Story...