I only interviewed at michigan, I know nothing about colorado. But I believe michigan is a great place if your someone interested in doing research and maybe one day following you dental degree with a PhD. If research + PhD is your goal, you have to pick michigan, simple as that.
I have to warn you tho, michigan out-of-state tuition puts people in shock lol and to make things worse, michigan is one of those states where, even if you change your residency to michigan resident, the school will still charge you out-of-state tuition for the entirety of the 4 years