Bigger CAN be better, but as you said, is not always so. Why? I dunno. Maybe it's tied into Freud's Oedipus Complex along with a fondness for big bums and tight lady parts.
What IS important (aside from personality and compatibility and all the "true love" bollocks) is a pretty face. If you're good to look at face-wise, it won't matter if you're an A-cup or on the heavier side of if you just so happen to be partial to a guy's secret fetish of glasses, or bondage, or dainty feet, or liking it in the back door, or doing multiple men at the same time, or other women, or involving clueless farm animals, or whatever. A winning smile, pretty eyes, well-kept hair, and a shapely nose can make up for a lack of curves or disgust at the thought of wearing a maid's outfit or embarrassingly masculine voices or even acne. (But don't forget that personality, compatibility, and "true love" part either.)
Now the obvious next question is, "How do I know if I have a pretty face? What defines good facial features." For that, I have no definite answer. That's purely objective.
So honestly, don't worry if your tit-tays resemble mosquito bites, just make up for it in another area of your body, preferably your face.