Well, many like large ones, but actually some men fetishize small-breasted women or like all breasts and have no preference.
Biologically speaking, this human male breast obsession is pretty weird. Men are the only male mammals fascinated by breasts in a sexual context. Women are the only female mammals whose breasts become enlarged at puberty, independent of pregnancy. We are also the only species in which males caress, massage, and even orally stimulate the female breasts during foreplay and sex.
Women do seem to enjoy the attention, at least at the right moments. When Roy Levin, of the University of Sheffield, and Cindy Meston, of the University of Texas, polled 301 people including 153 women they found that stimulating the breasts or nipples enhanced sexual arousal in about 82 percent of the women. Nearly 60 percent explicitly asked to have their nipples touched.
Men are generally pretty happy to oblige. As the success of Hooters, “men’s” magazines, a kajillion websites, and about 10,000 years of art tell us, men are extremely drawn to breasts and not because boys learn on the playground that breasts are something that they should be interested in.
It’s biological and deeply ingrained in our brain. In fact, research indicates that when we’re confronted with breasts or even breast-related stimuli like bras, we’ll start making bad decisions (and not just to eat at Hooters).