I prefer them small, but maybe that's because my wife has big 'uns, if she had tits a little clearasil could cure maybe I'd like big 'uns
I think a lot of surfers go to the web for what they don't have. I'm an ass man really, so as a surfer that's what I would be looking for immediately after the pretty face caught my eye.
As far as marketing I think natural gives you an extra selling point, but I've never really marketed fake tits as fake tits, just as big tits.