When we bought the girls' bunk bed we decided to get a twin over double. We said the double bed was so they could have a friend spend the night, but in reality the girls use the double bed every weekend. As much as they like their own space, they still like to sleep together.
What's really cute about them sleeping together is they do something I can only describe as synchronized sleeping. When I check on them before going to sleep they often have the same arm over their heads or are curled in the same direction. It's adorable.
Sometimes they are so different it's hard to believe they are twins. When they are synchronized sleeping it is a reminder that they are more alike than they are different.