Most important is functionality. Other than protection (totally covered cover) little else matters besides those two, least of all how it looks. As mine rarely leaves the house, it could be pink and say "Property of the Soviet Ballet" on it, but if it protects the iPad and works the way I want it, I'll buy it.
Mike
I picked functionality but also look for a slim, lightweight design. Mainly looking for some protection but also has to have a good typing mode.