I have always said my favorite kind of tits are the one's in my hand or mouth at the time.
That said a nice B-C cup is great, it really depends on the girl's body type. Like skinny girls with massive racks look odd to me as to curvier women with small boobs. I have dated girls with little ones and liked then and I dated a girl that had GG's. The GG girl was 21 at the time and they would stand on their own and looked fantastic. I had a lot of fun with them, but even she admits when she is in her 40's they are going to be down to her waist.