An avid home baker tested KitchenAid stand mixers for power and durability. Top picks mix delicate egg whites, gooey cookie dough, and bread doughs.

I bake a lot of sourdough bread — over 1,000 loaves in the past four years. Every six days or so I pull four one-kilogram loaves out of my oven, piling my counter high with deep brown batards that I ...