Personally, I prefer cup sizes ranging from A to C. I think once a woman's breasts pass a certain size, that they become less attractive. :<
As a friend once told me..."D-Cups are great, until you get bored and want some nachos" xD
Once you get past C cup, they're less of an attractant and more of an obstacle. It's male nature to like huge breasts. I suppose it's just an instinct...bigger breasts means healthier kid? Who knows? Don't quote me on that one. xD
Anyways, I'm against a woman getting a breast enhancement just for looks alone unless she's a teeny tiny A cup at age 18+. Then I'd say, well as long as it's not just for making yourself more attractive...then go up a cup or cup and a half and be happy. (This is where the whole self-worth thing kicks in, if she feels worthless because of her breast size, why not let her have a small step up if she's thought it through?)
With all that being said, I don't let a woman's breast size turn me on or off alone. I take in other factors such as overall appearance, does she USE what she HAS? ect...ect...
Personality is a greater factor to me though...I derive no enjoyment from a woman's company, no matter how fine she is, if she's a complete and utter ***** or any lesser form of such that I find intolerable. I also prefer that they be somewhat intelligent. I can usually tell that though just by getting to know them. :3
...Of course being bisexual, I feel quite the same about men. Their physical assets are not important to me overall, so long as they appear to be taking at least decent care of themselves. They don't have to be buff and muscled.
Overall, I don't grade too harshly on physical appearance unless they appear unhealthy.