Background: My (40sf) husband (40sm) and I bought a 3-bedroom house a few years ago, shortly before the panini. We of course took the master bedroom, and the other two bedrooms went to our children (then 12f and 10m).
We put a very nice double bed in the larger room, and a single bed in the smaller room, and told them both that they could choose their rooms, but whoever ended up in the larger room may be asked to share or relocate for visiting family members, while whoever ended up in the smaller room would have it to themself always.
We almost never have family over (hubby and I are both only children, and our parents are in other provinces), so we were surprised when our older daughter chose the smaller room, and our younger son chose the larger room. But ok, they worked it out between themselves, both seemed happy with the choice, so ok. And it has remained that way for a couple of years.