I voted for SimCity, not because it was the bigger failure, but because it really crapped on a franchise with such a legacy. I mean, SimCity is up there in the pantheon with Pac-Man, Super Mario, and Tetris! To make it worse, they have done four previous SimCity games that were legendary, and they managed to screw it up so, so much! The game mechanics were written in stone, man! IN STONE
It could still be fixed though. Offline mode, larger city sizes, no inflated population, fixed AI path finding, we might have a contender after that.