My cousin has installed whole house generators of both these brands for 20 years as well as servicing both brands during that time, and his experience is that Generac units have more problems than Kohler units. He also told me that a Kohler 14 kva unit will put out (start) and maintain a higher output than a similarly rated Generac unit.
GE makes light bulbs and air craft engines. When one of their light bulbs burns out I don't fear my flight going down.