you'll prolly get more clinical experience and see a wider variety of cases at UDM. Their clinical facilites are also brand new.
Michigan was generally higher rated mostly because overall it's a better school and gets way more in research money (but ratings aren't done anymore for dental schools).
UM also has more graduate programs. UDM only has endo and ortho. UM has OMFS, peds, perio, endo, othro, pros, oral path, PH.D, numerous masters programs (occlusion, biomaterials, etc) as well as GPR and AEGD.
As for in vs out of state, both schools have sizeable contingents of out of state students. The numbers from the class of 2004 (which are the only ones I have, check the latest admission requirements book for updated numbers) are 55/76 in state for UDM, and 55/106 for UM.
Hope this helps