They're essentially the respective kitchen power tool brand equivalents of Ryobi and Festool. The KitchenAid looks better, is designed for simplicity and approachability, covers the typical uses of a home kitchen, and sacrifices high-end power for flexibility as a multi-tool.
The Kenwood is larger, heavier, and more difficult to clean and maintain. Its size gives it a larger capacity that most households won't use. It costs 2-4x more than the KitchenAid and AFAICT comes in only the stainless steel finish. Most of the power available to the Kenwood is useless to home cooking and baking.