Welcome to AF
What machine are you currently using?
Do have a mobile service or fixed operation?
Hot water extractor will do the best job.
Look for atleast 140" water lift, two or three stage motors, & spray pressure of 100psi. Heat can be either internal tank or external line. Consider purchasing the largest you can afford, this avoids re-filling/empty time. If your mobile look for a nice lightweight unit unless mounted inside van, inside pick-up bed, or in traler.
Carpet extractors
www.topoftheline.com
www.rightlook.com
There are much better deals than those sites - you must find that yourself.
I have a small karcher cold water extractor & also a large heated extractor(mytee). I have heard people say Mytee is no good, but I havent had a problem with mine in 1 year - runs almost every day. I purchased both units from a Detail Shop going out of business.