For me I don't mind, I've felt meany of different shapes and sizes, ofc prefer a D but I'm not going to complain with something smaller also don't mind them bigger like a DD, E or bigger.
I, personally, am not to picky about size. The thing I want, is access to them. I saw the perfect ones, once. Skinny blonde, but a D cup in a lacy bra with a sheer button down white shirt. Face of an angel. Saw her for about 10 seconds and that image is burned into my mind forever.
I mean, both of course, but I always appreciate a nice ass, especially one that is firm but not huge, a nice modest firm ass with small to modest sized tits would be ideal.