We have tried them all (except for a greenhorn) and so far the Hydrosonic wand is the best. We no longer have to prescrub on border line carpets and dry times are great. The only down side for us is the 12 inch cleaning head.
I did order a Greenhorn wand Friday from Greenie and can not wait to try it. We clean thousands of apartments a year and the 14 inch head greatly helps with production times. I am also very interested to see how the high flow will perform in the nasty apartments we do.
The price of the Greenhorn is going up by $50 in April so if you are interested you might want to get one soon.