How many portions do you usually cook?
I usually cook 2-3 servings (recipies can range anywhere from 4-6) and I have been fine with my 5 C Kitchen Aid. I think I'd get the 7 cup with the small workbowl accessory if I did it all over again.
Unless you are cooking for a ton of people, I'd find the 11 to be too cumbersome to get in and out each day. The 5 is nice b/c it's small and I don't feel like it's a big production to use it.