Dammit late for the party again.
This is actually an interesting question HC.
Perhaps i can offer some insight on the human species in general. We are biologically hardwired to seek the best mate for reproduction. From this follows that we would find the finest physical specimin to pass our genes on with. What is defined as the best specimin however is largely cultural. For example in many cultures (and our own until somewhat recently) more amply proportioned people (ie Sumo wrestlers) were very highly regarded beacuse of their ability to weather shortages of food. However as regular nutrition becomes a reality for everyone, and with the recognition that obesity is acutally quite unhealthy, our view of the best potential mate has also changed. It can be for this reason that many of today's youth would prefer someone who is thin and fit, whilst the older generations (especially those that know all too well the pangs of hunger), look for those that can weather such a storm. This is not to say that gross obesity was or is desirable, but one need only look toward renaisance art to recognize that the perfect female form (as percieved at the time) was once far more ample. Another important recognition one should make, is that humans inately, wether we realize it or not, love symetry especialy in our mates. Though this is hard to show without a lenghtly discussion, in general those whom we find attractive, (People such as brad pitt, or Jennifer Annistion for example) acutally have very symetirc features. Youthfullness is also a measure of fertility and therefore again a factor in determining what would make good reproductive material and therefore is pleasing to the eye. (note since long hair is only found in people who are quite healthy this might explain our general tedancy to prefer long hair.) There is much more to say about this but lets see how it relates to breasts.
Following the line of argumentation given, men are looking for women who fit our societary ideal of fitness. Our society today in North America values slim, well defined, low bodyfat people. This translates into smaller breasts. Furthermore youthful breasts are in general more "perky" and this would go some distance in explaining why some prefer smaller sizes (more likely to be perky and therefore appear youthful). Finally though no-one has said it expelicitly (conatined implicitly in shape arguments), wether males realize it or not, symetry is one of the chief factors. As an after thought many males also like areola that are pinkish in colour, again a sign of youthfullness.
Please note the above tries to adress general themes that flow through our society and in no way is meant to tell anyone that their choice is wrong, or against natural tendancys. Beauty is in the eye of the beholder and this simply fact is what saves us as a whole.
I would also like to give kudos to the mods for allowing this thread to stay open, even as I am convinced that if I were to make such a thread about the physical features of the male anatomy it would be blasted to the database in the sky faster than I can say ban.