I agree with Fluffy (damn it, the pictures threw me off) - if it's natural then it's dandy, but if you're not able to get the job done.... well...
But as far as breast size? I think it matters more to the girl than the guy, most guys I know like boobs in general. Girls, I've met some who detested theirs because they were mistaken as boys or, conversely, they ended up nearly giving themselves black eyes every time we drove over a speed bump.
Nice mediums are really key, in other words.