Probably Stay but its really hard to choose. Stay has a load of replayability though and is a very polished game.
Eh, I am a poker junkie so I always come back to HoldEm even today. I think that game and Shazam are the two apps that have been on my iPhone since the dawn of the App Store and I've never deleted them.
Definitely Canabalt, Flight Control, and Doodle Jump. Three very awesome pick up on the go games for when you need to pass some time . Also, There's Geodefense Swarm coming up right behind those
Caster 4x4 Jam Alive-4-Ever I Love Katamari Payback Car Jack Streets Gangstar: West Coast Hustle DinoSmash Cocoto Kart LOTL Baseball Superstars 2010 Midnight Pool Otto-Matic Star Defense Epic Pet Wars Inkvaders The Rolando series Doctor Awesome Taptap and Boomer's SkyFishing I have too many favorites.
Right now I'm playing CHess Elite, (my most used app in the past 4 days) and Quantum Collapse. I cannot imagine life before quantum collapse.
Defender Chronicles - i've spent more time on this than all the other apps put together, but because of the recent bug, i lost my save data so i have to wait for the update So, for now, I'm really liking Dungeon Hunter