We gave our 3 boys the biggest room in the house. It made sense to us because they have a bunk bed in there and crib (later a twin bed with a trundle) and they play up there during day. DH and I are only in our room at night!
We have 3 bedrooms (ours, guest, and boys' room). Our daughter will have the guest room when she's older and we'll just boot her out of it when we have overnight guests (thus the trundle bed in the boys' room). I know they could all share the big room, but My dh and his sister shared a bed till he was like 9 and she was 12 and then shared rooms after that, but he hated it. With her being our only girl and my boys being sooo rough and rowdy; I want her to have a girly space for her where she can get away from their antics/michevious-ness.