You can get a sense of motor reliability at https://pedelecmonitor.wordpress.com. It is in German but includes a Google translate option on the right. You can sign up on the web site and record your current drive system, motor type, and mileage (in km). The web site tracks the mileage and motor repairs and you can see the data back for those it is tracking. For road applications Bosch seems to do very well (look at the 2nd generation motors in "Trekking" application"), as does Yamaha. Brose is distinctly worse, and Bafang mid-drives worse yet. There aren't enough Bafang hub-motor posters to tell how well they fare (which is a bit surprising as they are very common in the US).If reliability counts Bafang is not at near the top of my list. Yesterday I spoke with the service manager at a LBS that specializes in Ebikes and I asked him what he felt were the most and least reliable in his experience. He said they just returned a bunch of bikes with Bafang motors and put them as the least reliable of the bikes they sell. He also said the Specialized bikes with Brose motors were his personal favorites.