I think the RX-20 kicks some butt
But I don't think it should be used on commercial carpet. I think you run the risk of de-lamination. (or so I've heard) If you do use RX-20 for commercial, use the Hi-Dry head or switch out your jets and use the
glides.
The biggest problem with the RX-20 that I have found is keeping it balanced. You whack it once across a corner, not only have you damaged something, but the machine wobbles. So then you replace an arm, and it still wobbles, after you replace another three arms and it still wobbles, you end up buying the whole star replacement for the same price as three arms. Plus, Hi-Dry head cost about $850, and the head is a pain to clean.
I don't know much about the Roto-Vac stuff though.
Hope I helped.