What is difference between having sex with girls with big breasts and small breasts?

Not much. My husband finds bigger breast more attractive to start with. But he enjoys sex equally.

My husband like bigger, round non sagging boobs of our neighbor friend very much. Compared to me she has larger size breast. He used to stare at them. But when started making sex, it was overall just as good as me. There are some differences. He enjoys keeping his head in between her boobs very much and likes to get hit on his face with her boobs. But he finds it difficult to fully grab the boobs. Sometimes, it feels suffocating for him to such her boobs. Though she too enjoys her boobs, it is little difficult for her to handle the tight fit dress up and proper sizing is an issue for her dress up.

I have normal to big size boobs. Sizing and fitting of dresses are not big issues for me and so I usually wear open and tight fit T-shirts and shorts. When my husband fucks me in missionary style he can hold me boobs properly. When he fucks me hard in doggy style, he holds my boobs to keep me in fixed position. Finally boobs size can just matter in initial attraction and lovemaking but it does not count when making a fucking hard sex.