Efficiency is an ambiguous term in this usage.
Energy transfer from stored to mechanical
Is optimal when the voltage and current are
closest to equal.
Because of this you would think the optimal
case would be a multi geared motor.
Unfortunately, introducing gears introduces
loss of energy to heat and increased weight
which costs you as well.
I believe they rate the motors in kV/rpm, but
none of the bike motors give that value.
In general higher kv/rpm motors have to
get geared down to a usable rate.
With all things considered, I choose simplicity
as the deciding factor.
