Depends on what I'm playing. Usually, a good story will make a game with average or slightly below average gameplay a good game, and vice versa. But if one is going to be truly awful, I'd rather it was the story. A great story can't make up for truly awful gameplay, but great gameplay can make a game with shitty story fun to play, but horrible gameplay is a game-breaker for me, no matter how good the story is, I won't enjoy playing.