There are some things to consider depending upon the model you want. Bosch and Kitchen Aid w/ the 6 quart bowl will both make 6 loaves of bread at a time and do a good job. However, unless you are getting a used Bosch on ebay or elsewhere, know that the new Bosch is 880 W while the KA is 550 - incidentally that is the same as the older Bosch machines. Both are well made, both will last if not abused (and that is open to interpretation as they will both hold up to quite a beating).
My family has used both of these machines with good success - my mother has a 31 year old KA (5 qt. version) that she still loves and has never any issues. We bought a 35 year old Bosch 10 years ago (so it's 45 years old now). Now, I am in the market a the moment to replace the machine. DH is an electrician and a generally handy guy, took it apart and mentioned that if the bearings were still good, the bushing on the motor would last for several more years.
The two brands already mentioned are the only two I am considering. I am leaning toward the Bosch only because that is what I last had. BUT if I can't find what I want on ebay as I am without a mixer at a time of the year when that really isn't cool, I will either order a KA or find a 6 quart version in the stores this weekend so that our family can make the cookies and breads that are part our holiday traditions. Do note that a new 6 quart KA will cost anywhere from $300 - $400. The Pearl Metalic 6 qt KA on Amazon is $299.99 and has free shipping - at least, I do as I am a Prime member. The lowest price of other colors that I have found is either Amazon or ebay. The only place that I have found a deal on brand new Bosch mixers is on ebay, though there are fewer available since we are so close to Christmas. However, Pleasant Hill Grains has a good deal. I just haven't been able to hit on a couple of the other sites I trust. I will update after I've had a moment or two to check on it.
Hope that breakdown helps you a bit - it may be way more than you ever wanted to know about either of these two mixers.