Once you have a few choices in your price range you need to get down to the details of the machine. The dough hook is vital in your kneading of the dough. There are two basic shapes, so what is the best shape to knead bread?
C-shaped dough hooks tend to ride up the hook or the sides of the bowl. That results in the gluten to develop uneven. You will have to constantly pull the dough back into place during the operation.
S-shaped dough hooks usually give you a much more even mix to the dough hence a more even gluten development. If all the other factors are the same like the power, quality and size. Go with the mixer that has more of an S-shape dough hook.