That's your opinion. The last "memorable" game against Minnesota was the 2007 West Regional Final. Since then, we've had several races with Denver for the MacNaughton, a couple meetings in the Final Five, including last year's 2OT thriller, and an NCAA Regional Final. On top of that, we had the 2003 WCHA First Round, which was epic, and the 2004 Regional Final and 2005 Title Game. Throw in the Robbie Bina incident, Jesse Martin incident, Gwozdecky dancing on the dash boards, and running out to center ice, and I think the DU-UND rivalry is bigger than UM-UND. FWIW, I don't think the majority of Sioux fans agree with me, but I do think many of the diehards feel the same way that I do.
Historically, I would argue that UM-UND is the biggest. One of the two teams has been at the top of college hockey since forever, and more often than not it is both. Denver basically sucked for 35 years.