Appearance-wise, of course bigger is great. But when it comes down to the nitty gritty, it depends on the person, I'd say. It's only in the past few years I really grew to love big boobs and have a ton of fun playing with them, but I can appreciate a girl with smaller boobs and still have a great time with them. The same with booty too. It's a huge turn on to see a nice onion, but in the end it's not necessary to have an overall great time and session.
For me, at least.