My gf likes it best on her stomach when I don't enter her all the way and just watch her lips expand to the sides. She likes to call it "being comfortably stretched". She can barely take 6 inches of length and doesn't like the feeling of being jabbed by a thinner penis, so she votes girth absolutely. I'm not huge, 7"x6", but even with the experience of fucking or sucking 20 or so guys total, she hasn't had or seen thicker.