I have used multiple GPS navigators and I am convinced that their routing algorithms are all equally bad. The problem that they all seem to share is that the routing algorithm has no concept of a pain in the ass factor. A particular route may be shorter and/or faster but when it has stoplights on every block there is no way it is going to be faster than a slightly longer or out of the way road without lights. A particular 2-lane country highway may be a shorter potentially faster route than the interstate, but when you get trapped behind RVs, tractors, retirees in no hurry, etc. then it takes a lot longer.
It would be trivial to encode a pain in the ass metric using fuzzy inference and utilize it in routing algorithms. Maybe some of the higher end GPS navigators have this feature but I have my doubts.