IMO, oral sex is definately sex and even more intimate than vaginal sex, since you're putting yourself in the hands of someone who's explicitly focused on pleasuring you.
Every guy wants to hit a hot girl; but when that girl has boned somebody else, she's a slut. c'mon..IMO when the girl has more experience is better. Not something like 50 men but enough to know what is good and what sucks. And for an experienced girl, YES, SIZE DOES MATTER.