My collection is a little bit of everything. Big into 80s pop/rock/R&B, country from the mid 70s to the early 2000s, disco to current EDM/club remixes, sprinkled in with a little jazz, a little classical, a little early rap (nothing after about 1992 speaks to me at all, aside from saying "not this"), a little classic rock.
My two favorite XM stations are First Wave and Utopia, with Prime Country and Hair Nation a close third and fourth.