Whatever motor brand your local favourite bike shop services should be high on the list. Not much good if you have to ship yourself to timbuktu to get service or parts. Here in Ontario Canada we never saw Yamaha motors for the longest time, although I have heard good things about them. Have not heard who is the authorized service centre for those motors, which from my experience means more. Some motors are smoother than others, some more gutsy, etc., but it still comes down to can you get certified mechanic working on it if it hits the fan. Shimano, Brose, Bosch all seem to have service available here.