Girls, your boob size only matters to me if the size of my manhood matters to you. Just kidding.
If we're going to be discussing favorable physical traits though, we might as well cover more than just breasts. Here are my thoughts on the matter. First of all, I don't consider myself to be a shallow guy (hopefully I'm more on the deep end) therefore physical characteristics are not nearly as important to me in partners as the personality; Physical beauty may catch my eye, but the soul and spirit of the woman are what keep me with her.
Now in all fairness, I believe everyone must be physically attracted to a partner enough to have interest. I find a lot of females immediately attractive though, so it's not that hard to gain my interest. I also have a soft spot for short girls (5'0 - 5'5) burnettes w/ brown or green eyes, though it is not really important. As long as they're shorter than I am (6'0) it's fine. I think petite girls are generally the most attractive, and they obviously don't tend to have huge boobs. Anything from A-C is ideal. Also, I would think most girls would weigh less than I do, especially if they're shorter than I am. When I say petite is attractive I mean small but not skin and bones. Anywhere from 100-150 lbs. is fine, more or less than that range is probably unhealthy.
It doesn't really matter, but being average weight for your height and age is usually the most attractive and healthiest, in my opinion.