Mostly people who are really into music, which is cool, and are chill. I had a flat mate once who was into metal, chill guy but not great as a flat mate (nothing to do with music, just flat mate stuff). I know some subsets of metal draw in people who are the bad kind of weird, but I haven’t (knowingly) met those. TBH I haven’t met a metal head in years, though (at least not knowingly).