The larger cities in Montana certainly have the qualities of typical "great" downtowns. You'll find a density of business, culture, and retail in Missoula, Bozeman, and Billings, but in Montana, I don't think that's what necessarily makes the "best" downtown.
There was a time that you could really fly on the highways in Montana, but all good things come to an end. So, where does Montana rank for speeding tickets?