tOSU. I lived in Michigan for many years, and if anything I think BYU-utah is more intense, and stirs more emotion, even if it is much less famous nationally.

In fact, from the Michigan perspective I'm not even sure that tOSU is really their biggest rival. Seemed like Michigan State is at least as big a deal to them overall. Much more so in basketball, slightly less so in football. But more importantly, the fans cross paths every day and are related to each other, like BYU-utah, which creates more friction and emotion.

As for Texas, I have less direct experience there, but my Texas fan friends seem to hate Texas A&M more than Oklahoma. Maybe this is changing now that they're in different conferences, but I don't know that Oklahoma has pulled ahead. I don't think of Texas-OU as being more intense than BYU-utah at all.