It's tough.
I think Minnesota is out. Not the top team in the West, despite equal record to Wisconsin. But Wisconsin had to play OSU, and Minnesota didn't. IMHO Wisconsin's win over Michigan is roughly equal to Minnesota's win over PSU, but Wisconsin has H2H over Minnesota.
That gives you PSU and Wisconsin. Wisconsin IMHO has the worse loss, losing to Illinois while PSU lost to Minnesota. But I think both team are worthy.
For me it's a coin flip.
So I'd go Wisconsin. I trust their monstrous OL to beat the skinny fast kids from Oregon in Lawry's Beef Bowl, and that's something.