After years of renting Rug Doctor from Home Depot, I got this one:
http://www.amazon.com/Hoover-MaxExtr...dp/B0013YPWE6/
It works much better than I expected on the carpet; about as well as the Rug Doctor, I think. The attachments don't have as much suction as the Rug Doctor version, and the spinning brush on attachment is barely useful. Tank is decent size, but not as large as Rug Doctor.
On the positive side, no more renting and having to clean a rental of someone else's pet hair, pubes, grossness, etc. before bringing it into my house. No more having to haul a rental machine back and forth and getting rental unit juices in my trunk carpet.
I put hot water (hot out of the tap) in both the Hoover and the Rug Doctor. I've seen some versions that claim to heat the water, but I think it's BS.
The carpet cleaner detergent that they sell at Costco (it was Bissell branded the last time I bought it) is always the best deal unless you go with the Zep brand at Home Depot (which I've never tried).