I would avoid the Missoula and Whitefish areas. Missoula has some nice country around it, but has a very high population of greenies. Whitefish/Kalispell seems to have been hit with an influx of California out of staters (and mostly not the good kind). Too bad too because there is some good riding near both places I'm told.
As said, the south east corner of the state isn't anything special. I currently live in Billings and it is as far east as I really want to go. Plenty of work here, but it is pretty crowded and gets HOT and dry in the summer time (worse than any other place in the state). Prices for things like vehicles and real estate are starting to be driven up by the oil field money to the east. Good dirt biking areas to the south of town and into Wyoming. 3hrs to Cooke City, 2:15 to the Big Horns, 3-3 1/2 to the areas south of Bozeman, 3hrs to the Belts.
I went to college in Bozeman for 4 years before moving to Billings for work and would move back there if I got the chance. 3 sledding locations about 1-1:15 south of Big Sky, 1:45 to West Yellowstone, 2 1/2 to Island Park, 3 hrs to Cooke City, 2 hrs to the Belts, and the Bridger mountains are 20min but the riding is fairly limited there. You will run in to quite a few greenies here too, but the hippie to off road enthusiast ratio seems to be staying tolerable. Only downside is there are no moto tracks left in the area that will let me ride my quads on them
Lewistown is also worth looking at IMO. Not a lot going on in town for big excitement, but the surrounding country is really nice. Good hunting in the area, ATV, RZR, dirt bike riding. Belts are about the closest sledding, 1-1 1/2 hrs away, areas south of Bozeman are 3 1/2, 4hrs to the Big Horns.