This was suprisingly difficult question to answer mainly because I really haven't thought about it. I went with bedrooms but please note that for many of my Sims their bedrooms double as an office/desk area as well especially for my teens and as I have a lot of roommate situations where the bedroom doubles as a lot of things for my Sims. At least two bedrooms double or tripple as a bedroom/office/livingroom. In one situation its because said sim is a loner and rooms with 2 outgoing Sims he doesn't really like and the other is a mother and son toddler who live outside the main house in a houseboat kinda thing.
Bedrooms can also be most difficult for me to decorate because I like to decorate the bedrooms in what ever the personality, hobbies and interest the Sim has and is but sometimes it takes me a long time to see it. Sometimes never.
