To be honest I've found the cheapest stuff works the best. I use Tuff Stuff which i get from Autozone. It's like 1.99 or something but does one hell of a job with just a little elbow grease and a dry towel.
get any decent spray on foaming carpet cleaner.....OR you can even get the cleaner that goes in those machines you rent at the grocery store...mix with some water in a bucket....get a scrup brush...and go to town....then hang to dry....works like a champ!
never clean them. they are always clean. went to a hardware store and bought a clear plastic mat and then cut it to size. when needed i take that out, hose it down, let it dry and my mats are always clean. sometimes i sit in the car barefoot at night listening to the radio and its nice to feel clean thick carpet under your feet