I think the Euro Leagues are much more popular here than the MLS is, which is actually the case in most of the world.
Most domestic leagues have poor support, even in countries where soccer is the dominant sport, more people follow the famous Euro teams.
The one thing the Euro soccer leagues have over any American sport is that whole deal where the worst/best teams at each level move down/up to the appropriate league. That is just plain smokin’ cool.
Manchester United seems to have a pretty fair fan base around here, perhaps because it’s our own city’s namesake (in NH).