I use ProTeam backpacks for commercial janitorial services.
They are strong, and have great qualities. Faster, lighter, hit corners well, and pickup most debris.
However, when it comes to carpet with pile, they aren't the best. Brushes will agitate everything enough for the suction to pick up what it needs to. I have several customers that know we use backpacks, and insist that we use uprights in their establishments.
One of these customers who said that told me to use their Dyson. I was quite impressed with it. It didn't have a beater bar (brushes) and allowed to go from hard floor to carpet without getting hung up. It also didn't mark the floor that other commercial vacs do.