Middrive would be more efficient IMHO.I am now rebuilding/modifying a SunSeeker EcoTad and installed a Bafang BBS02 750watt 48volt middrive after messing up my knee.This middrive has peddle assist built right in.For good measure I had a double walled 700c hybrid wheel laced up around the SRAM DDS 3 spd Hub and 11-34 9spd piggybacked to that.Im waiting anxiously to get it back so I can tack it for a nice long ride.