I've had both experiences. Last year, I had a roommate, which worked out pretty well. At the beginning of the year, I told her what to expect from me and both of us knew what was going on. It was good and we both granted each other privacy when it was needed.
This year, I have a single room because our campus has both single and double rooms available to students. You just have to talk to the guy who is in charge of housing and if there's any complications, he'll sit down and talk to you in more detail later. A lot of students (upperclassmen mostly) get single rooms because they know they'll have a lot of homework. A friend of mine has a single room because she goes to bed really late and gets up really early (and doesn't want to bother a roommate by doing this).
It mostly depends on what university you go to. Since I'm at a small school, there are more accomodations for dorm housing than at some of the larger universities.
Not that I spend much time in my room, however. I'm usually only there for quiet hours (when I'm resting or doing homework) or on the weekends. Oftentimes, I'm visiting one of my friends in one of the other dorm rooms and it's nice because it's almost all on-campus housing, so you can easily walk across campus in less than ten minutes to get to your friend's room to visit.
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Itaque incipet.
All that glitters is not gold but at least it contains free electrons.