Personally, I'm biased because I was born and raised here and thus am a fan of the Big Ten; thus, i feel the Big Ten is a more attractive conference to play in, especially now with Nebraska coming. CU also has the other in-state University (CSU) to compete against, which should be a factor.
That being said, despite having been born and raised here, I think Boulder is one of the prettiest communities around, is a short drive from Denver, and they've got some pretty sweet unis to boot. 2 million a year for five years would put me in a pretty nice little house at the base of the Rockies, and I could have my getaway condo down in the Bahamas as well.
I have ties to MN, so I would pick UMN, but if I'm a neutral party and am offered the same amount of money, I personally would go Boulder.