Some say that the whole state is like one giant Christmas town, but I think there are a few towns that have something a little extra that makes them feel special at Christmas.
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.