Boob size doesn't matter, and I've seen a surprising number of men say that they find big boobs disgusting and greatly prefer smaller ones. Some of these men said that even a C was too big.
Smaller boobs make a girl cuter, which many men actually consider more attractive than the usual "hot". One could say she was less curvy, but another could say she was less lumpy. Also, smaller boobs usually belong to skinnier women, which a lot of men consider attractive.
Bigger boobs trade the "cute" for "hot". A woman with huge boobs is noticed when entering a room. She has cleavage to show off, and is very, very bouncy. Men would pay profound attention if she were to jump. Unfortunately, most naturally well-endowed girls I've seen are very saggy due to the weight. Some girls with big boobs are also fairly fat, which isn't a good thing to most men.
In my eyes, the two extremes balance out to the point that boob size doesn't really matter. The only advantage that one side clearly has over the other is that big boobs can give tittyfucks. As much as I love boobs, that's clearly something I want, although it doesn't (at least I think it doesn't) affect my judgment when looking for women. Just because a woman is well-endowed doesn't necessarily mean she wants a guy to fuck her in the chest, nor does it mean she wants to jack a guy off using her boobs.
Blah blah blah, point is, boob size doesn't really matter.
