Best kind of cat litter - least odor?

I am wondering what people's experiences are with different types of cat litter. I am looking for a litter that lasts a long time and absorbs most of the smells. I have a small house, and although the litter is cleaned often the smell eventually gets throughout the whole house. I have heard good and bad things about the crystals and also the natural corn or wheat based litters. What is your experience? I have two cats. Any extra suggestions would be very helpful, thanks.