That's a question I received via Formspring and I thought I can answer it now. :)
First of all I have to say that I'm not sure how it's meant. Breasts in general, on women? Or on me if I had to choose? I'll just answer both possibilities.
On women: I can't say. I tend to say: Rather bigger than too small, but usually (and I admit that I'm a breast man) I see the "whole package" and if that fits I don't care for the cup size. A small girl can look great with B's as well as with D's ... so that's really hard to answer.
As for breasts on myself ... I think of breasts as the most prominent feeling that would remind me that I'm a woman now. I also can imagine how much large breasts suck after a while .... just seeing women who do sports, even in sport-bras. And plenty of women have told me that "problem" before.
So if I could choose, and assuming I'd have an average body otherwise, I'd probably go with a C-cup. But I have to say that in my fantasy I don't choose that myself. I'd like the experience and the challenge to get along with the bust I got ...
Like I said, the breasts are (in my head) the most prominent feeling that underline I'm a woman ... therefore I think that a C-cup would be appropriate.
I'd really suffer from ridiculous large (fake) breasts or something. In that case (speaking as my male self now) I'd prefer small breasts over fake breasts.
Wow, I never wrote that much about tits ... good I get to see my gf tonight. :D