I have big boobs and now that I'm pregnant they are colossal and let me tell you from a fashion perspective I find that they limit me..in terms of what I can wear.
I can't bring myself to wear low-cut items because it looks bimboish pammy andersonish. You want people to look you in the eyes not constantly talking to your boobs.
Smaller breasts presents more options imo..if you want cleavage for a certain dress/top..use a push up bra or boob tape
There is a thread about the whole cleavage issue :
http://www.thefashionspot.com/forums...ad.php?t=20610 
THIS imo is beautiful, sexy but most importantly not vulgar (from Br. Vogue) :