I know this is a matter of preference. I have a good buddy who has had good looking girls interested in him, but their tits aren't big enough for him. On the other hand, he will go for someone only slightly attractive, in my eyes, if they have huge ones. That's his kink, I suppose he can't understand why I'm a greek freak, but different strokes for different folks. I don't crave mosquito bites, but if they are proportional to the build of the girl, size A doesn't bother me, and I will play around with them, but in any case, that's not my focus, ass man that I am. Obviously, very stretched out and droopy is not attractive, but I'm fairly forgiving if everything else is in good shape. What bothers me the most is unproportional and obviously fake ones. In my humble estimation, a ninety-five pound girl with DDs, for example, looks most unattractive to me. I've chosen not to call some providers, even though their profile generally aligns with my prefernces, because they had too much up there for my liking.
The only turn-off for me, breast-wise, beyond being way out of proportion to a woman's figure is large, droopy breasts, on ANY figure. I much prefer small breasts to "knee-bangers". And I prefer natural breasts to man-made, although I know some providers who have augmented breasts that are difficult to tell from the real thing, visually or tangibly.
I think one of the most attractive and sexy type of breasts are those that fit nicely into a champagne coupe. Although larger, or smaller, are just fine with me also. 
I like all different shapes and sizes. The key to me is that they look good on the lady.
I've been with providers that didn't have much for breasts, but what they did have looked good on them. Conversely, I've been with providers that had man mades that were too big on them. In one case the lady had man mades that her nipples pointed different directions, I actually had to be sure not to look at them during the act because I'd start to lose my erection.
A lady, that I've seen numerous times, the first time we were together she shyly took off her bra and apologized for her breasts not being big. The thing is her breasts look great on her, she had mentioned that she was thinking about getting new boobs, when I didn't respond she asked what I was thinking, I said "it's not my business but I like them just the way they are". She seemed to like that, proceeded to rock my world and I've been a repeat client.
Now it's not to say I don't like man mades, some are done very well and I've seen before and after pics or videos and I prefer the man mades, others not so much.
Natural ones anywhere from a nice perky B to a nicely shaped C cup. Nit that I am turned off by smaller or larger, or even artificial ones. I like em perky with nips that poke through a shirt. This being said. Extra large tits on a gal can sometimes look ridiculous. Just as flat chested chicks don't look all that feminine. I like women, not caricatures. If you are too extreme one way or the other I am sure there are guys who will move heaven and earth to see you. Me, while I'll never pass up an option for free sex with a lady, I won't go out of my way to find one not to my taste and pay her.
I suppose that the other thing, other than size and appearance is the attention they get during play. I'm not a breast neglecter, even though that's not my main destination in terms of erogenous zones. I like working up a good titty boner, and doing some manipulation during oral or intercourse. Some girls could seem to care less for tit play (just like I find having my balls worked on too much to be vauguely uncomfortable, and it doesn't do much for me), while others seem to want me to act like a hungry infant. Whatever gets you juicy, girl, I'll do it, unless it goes on too long or gets too wierd. Can't understand the whole lactation thing as a sexual fetish. When my ex was nursing, I went on a dairy fast for about six months. EWW yucky! But to each his/her own mainly.
When my wife had the kids she didn't breastfeed with them. She went the formula route. As a working woman it was too tough to continue and pumping became a chore for her. She gave it the old college try and finally gave up. But For a few weeks there she actually asked me to suck her titties dry. Her breasts felt full and she felt she needed relief but the kids wouldn't latch on. So she had me suck her tits as part of foreplay. She got off on it and I have to say so did I. It was super sweet but sexy as hell. Not much came out. She dried up fairly quickly especially since we were doing it so infrequently and she had stopped both the pumping and the feeding.
thinner women - and on a size 0/2 body, Cs start to look pretty big, and larger - well.....
but breast size is not a make or break for me nearly as much as breast shape is -
I like firmness (not hardness lol) and a perky shape.....
I realized I wanted to see them all! Are some better than others? Yep, but I am an EOE.
Wasn't the first set of boobs you saw was your moms? 
after having intercourse for the first time. I was driving down the main drag in my city, looking at all the women and thinking, "every one of them has one of those."
When a girl walks up with a little bitty waist, and that round thing in your face!
You get sprung!
