Great topic!
I love old sculptures and paintings of women, back before body ideals became extreme. A lot of them featured modest breast sizes; large A's, B's, and the occasional C. With realistic soft hourglass figures that were proportionate to the rest of their bodys.
I would like enough boobage to have cleavage but think shape and symmetry is far more important than size.
For myself personally:
Minimum - full A
Ideal- full B
Maximum- full C
My favorite iS the brunette girl. I love her breasts. I'm not exactly sure what size she is (they said shes a B cup) but she almost looks like a C cup to me.