Best carpet shampoo?

[mineofuselessinformation]

I've just got a new machine (have just spent a happy half hour trying it in a section of my hall carpet), and need to get a full size carpet shampoo.
What have you found to be the best?

Pro-Kleen, Bissell, Rug Doctor, Dirtbusters????

Anyone?

I use liquid clothes detergent. The one the manufacturers supplied was rubbish. If your carpets are wool use a wool safe one, but otherwise use the stronger ones with enzymes.

I just commented on another thread about this- professional cleaners add a flame retardant. I am looking for this for next time and might buy online.