Not that bothered as long as there's something there. I don't like a completely flat chest that would be unattractive. If a had to choose between a fat women with large breasts or a slim women with small ones, then I'd choose the slim women.

If there was two slim near identical twins and one had small breasts and one had big breasts, I'd go for the latter. Overall though breasts size is not something I care much about. Face, *** and legs I look for first over breasts.