Storm overall, when it comes to quality and how intense it was. But GoT was the one that set it all up and put me in Westeros. Also, that intro! The Others (book Others, not white walkers from the show) creeped the hell out of me many years ago, and still do.
EDIT: I voted GoT since it has a ton of foreshadowing for R+L=J too. That tipped the scale for me.