IMHO it would be very difficult to accurately declare one is better than the other. Seems both systems work quite well. In any case with either system you have an electric motor providing the initial power by either direct drive eliminating the hydraulics or an electric motor driving a hydraulic pump. I am not aware of any slides that are operated by an engine driven hydraulic pump.
We have had both types also and both are mechanicallay reliable but the hydraulic slide on our Pace Arrow took up more storage space than the electric on our Tradewinds because of the telescoping arms using up a locker on the left side of the coach.