I had both at university - a single room for two years, then a two-room set for a year - and found they had different strengths. In the single room, I could go to my bed for a break, or to fetch something from over there, without completely losing my focus. In the set, it was nice to have a separate room for sleeping and keeping clothes (so I didn't have to worry about keeping them out of the way - they aren't taking up space in my work area). Ultimately though, I didn't find them to be fundamentally different, other than literally having more space in the two-room set.

Worth noting that I didn't cook in either - there was a separate (shared) kitchen, though most of the time I would be eating in Hall anyway, which may have been a factor.