Having run the range from AA to DD, I've figured out that there are really just two types of breasts in the world, large and small. The only effective difference between the two is what you can do with them. I'd classify "Large" girls as B and above, because in my experience the saying "more than a hand-full is wasted" has proven, for the most part, true. Now the girls smaller than that have fewer options. I'm not saying they're any less attrctive, or any less feminine, there's just only so much you can do with the lack of materials there.
Even having said all that, the real determining factor in how wonderful a woman can be is her personality, not her looks. I'm not saying this to win brownie points (how many women really frequent these forums anyways?), I'm saying this because even the greatest lay in the world can be repulsive just by acting like a bitch.
Oh, and I do love a fantastic set of tits.