In my first year, I lived in a mixed-sex flat. The guys I lived with were loud and messy, and this stressed the girls out and caused arguments. Things were never resolved properly, and there were petty arguments. I tend to get on with both males and females equally, but I found that in our flat, trying to get on with either sex, especially guys, was very difficult.
This year, I live in a single sex flat. We all get on very well, the flat stays tidy, and issues are talked through and resolved sensibly. Most of the girls are in relationships, and their boyfriends are over a lot, so there's often some male company - but since it's not their flat, they treat it with respect. It's a much happier environment for me this year; everyone gets on a lot better.