I don't use one personally but I've seen a couple of difference maintenance companies where I work and the back pack style seems to work much faster. The guys with the canister seem to vacuum much slower for larger areas. So, if you've got a large area to clean, I would check out the back pack style ones. Good luck!

It depends on the business and the carpet, and employees using it. backpacks work well if it is a flat, commercial grade carpet/barefloor, but they cannot be put down or the motor blows. canister - has incredible suction and cleaning ability because it can go flat to the floor. find a vacuum dealer /janitorial supply and TRY them before purchase.