I've only used braid/leader setups on my Pushing outfits. In those cases I would have 6# mono as a leader (and my main lines were 20-30# test).
As far as casting setups using braid, I don't use a leader. I tie my 10/2 PowerPro braid directly to the lure with an Improved Clinch knot. I only use the Improved Clinch once the braid has been used for awhile. When the braid is new & still has some slickness/coating to it, I'll use the Improved Clinch, but tie a double Overhand Knot in the tag end prior to cinching the knot down. That knot will stop the tag end from slipping thru the Improved Clinch when under the strain of fish pullage or pulling against a snagged lure.

The brand of leader line has changed several times over the years, but currently I'm using Vicious Panfish Copolymer 6# test.