What does the machine need to beable to handle? Specifications, expectations, price range, etc...? What is wrong with the current machines? Is the new machine for supplementing the other machines? What models are the current machines?
Extractors to look at:
Mytee HP60, HP100, Mytee Light w/heat or w/o heat; Mytee Products @ PAC
Century 400 Sensei, Tempo
Durramaid
EDIC Galaxy 3000
US Products Cobra
A machine to look at if you are at a fiixed location, have a dedicated circuit and extra cash is the Clean Craft Eclipse.
While I love my Century 400 Sensei, I believe that the availability of local service is the important consideration. Can your LOCAL dealer service the machine in a timely manner? As you know, even the best machine will rquire attention eventually.
If you are in a shop and can get enough power, then make sure you get a machine with the most powerfull water pump you can get. It really does help get the soap/dirt out of the carpets quicker.
I personally have a Sensei unit and really like it but I have to be mobile and it works well for me.