I vote for the 1990's-early 2000's style Hoover SpinScrub. Or whatever they sell now that is based on that design. I work on the Hoovers and once in a while the Bissell but I prefer the Hoover. Two examples: (1) The F5860, which has the spot cleaning hose that attaches to the waste water tank; (2) the F5866, which has the spot cleaning hose that goes through the base of the handle and locks onto a vacuum port there. There are many iterations of both of these.
People discard these machines often and it doesn't take much to get them going again. One problem is they don't clean them, and don't rinse/flush the system after using. When a carpet cleaning job is done, you don't stop with the carpet. You continue on with a clean-up of the machine including flushing straight water through both sides of the system (floor and spot cleaning).
Common complaint: The spot cleaning side doesn't work. Reason: Dried/coagulated cleaning solution in inner line of hose. Owner didn't flush it after last use.
On the F5866 type, they are notorious for breaking the hose right were it locks on to the vacuum port. This is because the hose makes a 90 degree turn at this point and the flexing (from handle movement) stresses the material and it splits, reducing suction to both sides of the system. These are easy to repair. You just cut off about three inches of outer hose and two inches of inner line, clean the dead material from the hose & line out of the black fitting, then epoxy the line in place, let cure, then refit the outer hose securing it with silicone silastic cement and allow that to cure. I drill the material out of the fitting where the inner line is glued into place before reattaching. It shortens the hose a bit, but it restores suction and functionality. I've fixed a bunch of these like this.
On this type, you've got to always leave the spot cleaning nozzle cradled to maintain optimum suction.
On the F5860 type, the spot cleaning hose is removeable. People lose this or the blocking spacer in the tank, then the machine is no good to them.
It isn't often that these have electrical problems; all they have is a switch and a motor. The scrubbers are run by vacuum from the motor. The scrubber brushes get contaminated with hair, fiber, etc, so I use a cat flea comb to clean them out.
People are careless and run into walls with these machines so you will see them with broken nozzles. Usually, this isn't a functional issue. Often it's just chipped corners and this has no functional effect. I can buy these machines often for $4 to $6 as discards and it doesn't take much to fix them up. Or you can find them sitting along the road on trash pickup day.
These machines have great suction and there are times when they can be used for other than carpet cleaning. Like when a water heater ruptures and water is in the floor coverings. You'd be surprised how well these work for getting water out of carpet under those circumstances. There can be issues with the underlying pad, and you can pull it all out and let it dry after you get the sopping water out. It's cheaper than replacing the carpet. Or just let your insurance company deal with it.
Always, always, clean the machine after use (did I already say that? I'm saying it again). You can even take it outside and spray off the underside with a hose; it won't hurt it; after all, it has water going on under there all the time you're using it anyway. Clean out the scrubbers -- they unclip and come off. Rinse out both tanks and flush both sides of the system with clear water.
If you don't like hair balls stuck in the clear plastic top duct from the nozzle, this comes off with about five screws, then you can clean it properly. Sometimes, you can get this clean by just blowing water back through the nozzle system with the tank off.
