I have two cats and I use the litter (silica) crystals as apparently they are very environmental ... plus they are the best with odour. They are more expensive but I only have to change each try once a week. Highly recommend.
In addition to the above, there is also corn-based litter. We use a 1/2-1/2 combo of the Feline Pine clumping litter (the "sawdust" kind) and Dr. Elsey's clay litter. Not as good as going all paper, or all pine, etc. but at least we cut the clay use by half. We had tried just about every type and this is the only combo we could get our cats to use. We use the Dr. Elsey's because its noticably more dust free than the other clay litters. It may come down to what you can convince your cats to use. Be sure to transition them slowly!