There is no such thing as one maunufacturer that makes everything well. Figure out what you want from each appliance and then go shopping they do not have to match but they do need to function for you I have a Bertazzoni range, a Bosch DW commercial fridge and freezer from Fridgedaire double full sized wall ovens from Kitchen-Aid because these were the ones that had the function I was looking for.

If you have $12,000 - $18,000 per appliance to spend you are welcome to work with any of the high-end German lines...they will get you anything your heart desires...or if you are in the "normal" range, you can do as Patricia has and purchase each product based on its own merrits. You will want to stick with the same "finish" (stainless steel, slate, black, white, etc) but the brand shouldn't matter so long as you have the functions you want.