As mentioned - depends on your favorite game type
I like Puzzle / Platform / Arcade - so in my collection I have the following
Arkanoid / Brain Age / LemmingsDS / Mahjong / Neves / Professor Layton - Curious Village / Tetris / New Super Mario Bros / Mario Kart / Video Game Hero / StillAliveDS & Elebits
The only other games I have are 'Nintendogs' and 'Animal Crossing' - but I have these mainly because my Neices & Nephew all got copies and like to 'share' collectable items when they pop round.