Heh, for me, I'd have to say that Bust-A-Move is my pride and joy. I love popping bubbles with little blue and green dino guys, it's insanely fun.
I've been able to get to round 32 without using any continues, so I'd say I'm pretty good at it. :P
That, and it's always the cheapest game there, at $0.25 per play.