I highly recommend the Bissell 9400 ProHeat unit for carpet cleaning. We have had ours for about two years now. We work from home so having a clean environment is important to us. Also, we have between two and four cats at any given time, and they manage to get dirt and grime all over. We definitely needed something to get the dirt out of the carpets, and our previous carpet cleaners just weren't doing a great job.
First, this unit has a built in heater. This is great! With other carpet cleaners the water seemed to turn lukewarm or even cold within minutes. With the ProHeat the water was always warm and doing a good job of getting the dirt to break up.
The scrub brushes on the front really do a good job of getting the dirt to shake loose out of the carpet. They even manage to get up cat fur that a thorough vacuuming isn't able to get up. It is really great that even hair that is deep within the carpet - that normal vacuum cleaners can't get to - are brought up to the surface with this unit.
There's a good carry handle on the front, I can bring this up and down stairs without any problem.
You can switch the unit to do just water, or a low or heavy amount of solution. I love these options. It means I can do a pass with the cleaner, and then do a second pass later with just water. That ensures that the carpet is left clean, fresh, with no soapy residue.
Highly recommended - this unit is great. Feel free to contact me if you have any questions about it! It is just amazing at how well it cleans. I definitely recommend that everyone clean their carpets at least every quarter. You'll be amazed at what your vacuum is missing - at how your carpet is affecting the air you breathe.