I much prefer 'short and thick' to 'long and slender'. Anything over 6" sometimes bumps me in the wrong place during vaginal sex(perhaps an ovary, but not sure) and can give me a sharp pain which entirely ruins the mood. Also, the thicker ones fill me up much better and give me something to squeeze around Position is also important, as some get the guy in deeper and others work different areas inside me.
Come to think of it, tho, I've never had a bad one, only good, better and best!!
P