The newer Little Green Machines, such as the ProHeat and the Auto Care have a stronger motor. The Auto Care model just has the regular brush handle and a brush/crevice tool which is nice for automotive interiors. Personally, I have a Little Green ProHeat which comes with the Turbo Brush because I couldn't wait for the Auto Care model to be released.
I really like my Bissell, but the durability is something to be desired. It can break easily if you're not careful (my ProHeat is my second unit) so don't let anybody borrow it. You also have to follow the instructions of using it properly, and rinsing the brush(es) after every use. The Turbo Brush is nice and I use it but I first always agitate the carpet manually with a separate carpet brush. And from what I understand, the heat feature is what ruins the spray nozzle which dispenses the cleaning product....my Turbo Brush nozzle already acts funky after only a handful of uses with Heat (even though I rinsed thoroughly in cold water afterwards every time!).
A Bissell is a cheap and effective alternative to a carpet extractor but I don't think it is as powerful. Either way, my carpets wouldn't survive with all the mud and stuff that gets on them from my job. Even with cleaning my carpet with my Shop Vac, Tuff Stuff, Grime Reaper, a carpet brush, and microfiber towels.....the Bissell just does a better job hands-down.