The school I hate the most and root against the most is and always will be Utah State. I've been in Logan Salt Lake and Provo for b-ball games, and I have never had a worse experiance than when I attended a game at the Spectrum. Those fans up there are by far the worst, I even hate them more than Montana fans, I would love nothing more than for Utah State to go winnless every year in every sport, thats how much I hate them, yes HATE.
I Dont hate BYU, but I dont like them, and I continue to find myself rooting against them ALL THE TIME, I guess the reason I dislike them so much Is the bias they get from the local media, they win one game and they're the greatest thing ever, It happens every year and it gets old.
I like Utah though, I have alot of Utah friends and the Utah fans where pretty nice to me when I went to a bball game when Weber played them, not to mention I've gone to lots of Utah games vs other Mtn West teams, and I went to a couple vs Gonzaga and Oklahoma. I find it VERY easy to root for the Utes.
GO WILDCATS.