I like ample female curviness in girls, easily as far as the overweight category (and you'd be surprised how many "normal-looking" girls are technically overweight). As for guys, I think more about muscle than I do about fat. I like (and envy) well-toned muscles in a man, and I notice his arms before his stomach, but when I do notice I think I prefer a bit more cushioning.
Obviously these are just first-impressions preferences, I've gone outside of them lots of times and there are much more important criteria for dating, but they are the tendencies of attraction I've noticed.