Stand mixers rated highest for heavy duty use are those capable of handling large quantities and particularly tough tasks, such as kneading thick dough.
These mixers usually come with medium-large mixing bowls (4-5 quarts) and multiple speed settings. On average, glass bowl models are reportedly more heavy duty than stainless steel or plastic bowl models. Price is evidently not reflective of the mixer's ability to handle heavy duty tasks; the price range of the highest rated products for this use is very wide, with some costing as little as $100 and others topping the charts at over $500.
Bosch and Sunbeam are considered the leading brands in this category.