I would have to go with being picky. When watching porn, if I don't like the way the woman's breasts look, I'll move on.
What do I like? I like pert breasts, not too big, probably less than a D cup. I like the areola to be dark (a nice chocolate color is the best) - and well delineated from the rest of the breast. I don't like it when the areola just washes out into the rest of the brease. As far as size, I like the areola to be quarter size when the nipple is not erect and dime size when the nipple is erect.
Fortunately, I am with a woman who's breasts match that description exactly.