I grew up in the days of BYU dominating the series, so I have an appreciation for the rivalry in different eras.. that being said, if the Utes were out of the conference championship contention (because of too may conference losses), then I would rate the BYU game higher than almost any remaining games (except for maybe big name teams like Oregon, Stanford, USC/UCLA, for example). But, if Utah is still in contention, then in my mind any conference game would rate higher.
So, it depends.. but, it still comes down to conference title hopes I suppose