In my experience, a long and straight penis can feel great but can also cause a lady to go "ouch, my uterus!" And if a guy is 8 inches or more then he can forget anything anal. My personal preference is for something in the 5-7 inches range, with a good girth (which for me is around 4 inches). For me, girth is more important because I love the feeling of being filled. I'm not overly concerned about straight or curved, although a curved penis usually has a better time hitting my G-spot, which can be a lot of fun.
But honestly, I think it's all about how a man uses what he's been given. I have never been disappointed in sex because of the man's penis - the two times I have been disappointed it was definitely by the performance.