To be honest, dunbarton's bgm kinda sucks, so its always turned off for me. but whenever i go run karu dungeon, rundal, or g19 stuff, i leave it on. It's really worth it.
Saga's bgm wasn't that bad as well, and they hyped it up for season 2. Sure, they reused some music, but...
Taillteann's bgm is also the best one out of the uladh towns.
and if you didn't yet, you should leave your bgm on in shyllien and hillwen (at the lower levels).