Like a lot of people have said, it depends on your frame, height, and shape of your breasts. I'm pretty short and have a slim waist. My shoulders are aren't too broad. Right now, I think a full C would look good on me.
Some people just don't look good with very large breasts. For example, look at Heidi Montag:
She looked perfectly fine before (although I think she had implants at that point too and later got them increased). Personally I think her new implants look ridiculous. They're humongous for her body. Can you guys believe she wants to get them done even BIGGER? :s
I think she looked good at this size (her boobs are fake here too, but this is where she should have stopped):
Anyway, it all just depends on what the rest of your body looks like.
As for guys liking fake boobs, I don't agree. I've never heard any guy say that they like how the look of implants; I've only heard the exact opposite. However, I do think that they like perky, round breasts, which not all women have.
The only thing I've ever heard guys say they find unattractive concerning breasts are large nipples. I've met several men who seem to find big nipples "nasty," but think small nipples are "cute." I suppose since women don't go around showing their nipples, it doesn't occur to them that some females have large ones.