My hubby thinks that bigger is better; I disagree. I like the "average" size of about 6 inches. I've had bigger & it hurt a bit. I've had smaller & it was nothing to scream about. I guess I'm just accustomed to around 6 inches.
Women only have nerve endings 3 inches in to their vagina's so the only effect that a penis longer than that will have is phycological! A nice size to play with though is 6 - 7 inches!