[Cuog]

My prefered method is a hex shaft while hardest to build it has the best long term benefit=== I have never sheared nor seen a sheared hex shaft, they can snap like any other shaft but they are i beleive the strongest.

While keyways are nice they have flaws such as loose keys and the key exploding since all the torque is applied at that one point

For practicality i would use a similar method to that which secures the tires to the axles of your car, there are four to eight pins which are parellel to the shaft and are inserted into the wheel, very strong(it can withstand whatever you car dishes out and i challenge you to build a competition legal robot that dishes out more torque than my 1979 Trans Am, so much that it can snap through and average hub built correctly and like i described)