I like the Hoover Dual V for carpet cleaning - it has very good extraction (leaves carpet much drier than others) and it has a separate detergent container from the water and a rinse setting so you can do wash then rinse pass with clear water to remove detergent residue. Also you can pour un-used detergent back into the bottle because it's not diluted into the water until used by the machine!

For HEPA vacuum people have different favorites but I like the Dyson canister vacs.