It is an ancient instinct. A woman with large breasts is a healthy and strong woman and is more likely to have healthy offspring. And they are less likely to die from disease. But with breast implants it's a bit useless.
I'm fine with small and flat chested even (hell yeah androgyny!) to average-large, but I really hate ridiculously large breasts. Especially on a ridiculously thin woman anime... (I'm sorry, but come on. That's not how it works. Usually.)
Average~ I'm gay so I don't really care much about boobs sexually but in art I prefer to see something like a full B or a small C, depending on body type. I think if they're too small or too big, it can detract from the piece. Unless the piece is entirely about the boobs, but that's rare..