I’ve been to Montgenevre in 2011 when Le Tour passed through. Very quiet place, right at the top of the mountain, even the day before the tour arrived. a real one horse town.
Very few places to eat but the road riding is great. I only stayed there cos I couldn’t get anywhere in Briancon which is a much larger town in the valley with lots more facilities.
Handy for Col du Lauteret and Galibier but it is right at the top of the mountain so you have a slog back home in the evening. You can cross over into Italy too
Saw the MTB slopes but didn’t get a chance to ride them.
EDIT: Stayed in a poky little hotel in the high street. Not much to write home about but they did let us keep the bikes in the room!