I'd say go with a concept one. If your using it commercially I would say try and find a non power drive model, I've never used one but I would say it might be slightly lighter. I Have a concept 1, powermax with electronic control, and concept II with push button electronic controls. I like my concept one with cord rewind the best, I don't find it terribly heavy and at the end just hit the button and the cords gone.
Having owned several sanitaires, I feel like you just can't beat the quadraflex agitator for all around cleaning, dust, deep dirt, lint, pet hair etc.... Mind you ive tried several sanitaire brush rolls. VgII VG 1 with beaters and Vg with only brush strips. They just never seem to get the hair. Plus I find the filtration with a HEPA A bag is better than the new ST style sanitaire HEPA bag. Mine still leaked dust down where the bag connects to the machine and on the inside of the bag where the dirt tube connects to the bottom piece.
However finding new brush strips for a concept and other parts is obv not going to be as easy as a sanitaire. That might not matter if your just using it normally and not commercially. Sorry for the essay
Colby