What's the best binding setup for ski touring?

It depends on the emphasis of ski touring. If you favor more downhill performance, the CAST bindings is the clear winner as it utilizes the battle tested Look Pivot Bindings for downhill skiing, however, its heavy weight and complex transition actions may deter people. If you favor uphill performance, a pair of tech bindings may be a good choice, as they are light in weight, although they may not be as reliable. A good compromise between uphill and downhill may be Atomic Shift Bindings, they offer close to alpine binding experience for the downhill while being relatively light.