My answer is : "that it all depends."
It depends upon the type of carpet, and even perhaps the amount of open space to be cleaned.
There are many times that using the right wand will be much faster and easier; other times that using the rotovac would be more advisable.
The deciding factor maybe if the operator has some extra spendable money, the more tools in ones tool box, the better.
Those are my thoughts.
Good Fortune to all;
Ed Valentine
cross-american corp.