My opinion... the size doesnt' really matter... my yorkie weighs 8 pounds and she's still "little" to me... i can still scoop her up with one hand. she's small enough to sit on my lap when i drive or sit at the dinner table or computer desk... she likes to sit on the kitchen counter while i wash dishes too! I wouldn't trade her for any other in the world!
she's my little princess.
and her size is just right to me.
I would say if anything more consideration is needed on the pups personality.