I've used various Hoover and Bissell units and also my Century/Ninja. Heh heh, I must have at least five or six extractors around here
The problem with most larger nozzles is that they tend to leave things pretty damp IME. I actually DIYed an adaptor to use a little Bissell nozzle on my Century just because it helps get more moisture out. The *wide* Century nozzle, made for household use, simply left things way too wet for me.
To my (pleasant) surprise, my latest Bissell unit, a "ProHeat" model that looks like an upright vacuum cleaner, is my favorite; I even prefer it over my Century.
I'll sometimes scrub nasty stains with carpet brushes on my Cyclo.
Important things I've discovered: Heat makes a *huge* difference. Professional carpet-cleaning chemicals work a *LOT* better than other stuff (including the Griot's Interior Cleaner that I'm otherwise so happy with). Pre-spotting, with an adequate dwell-time, can work wonders if you use a pro product. It's best if you don't get things so wet that you really saturate the padding. Rinsing is critical, and the hotter the better. I might even switch from plain (hot) water rinses to a rinse agent next time. Don't quit rinsing until you're no longer getting *any* suds out of the carpet.
Check the yellow pages, there's almost always a pro carpet cleaning supply place nearby.