The braid to flourocarbon leader set up came about as guys were looking for a finesse presentation that offers better strength and sensitivity than just running a main line of flouro or mono. To answer your question, the lightest leader you can use, or get away with the more bites you'll get. Ive seen guys go as light as 6lb on leaders. The past couple of weeks I have been catching fish using a 10lb leader of seagar invsix. I'm actually using this around grass, and although its not thick grass yet, the only time I have broken my line in the last couple weeks was on a huge catfish. But, in the past 3 weeks, I have boated many bass and landed 2 cats with one of them being 25+ flathead. The main line I have been using since last year is the YGK sinking 16lb braid. I am also using the "FG knot". It takes a minute to tie but it is very strong. My advice is to find a smooth braid you like- Power pro max quatro is another great braid, and play with the leaders to see what size works best. One last tip I would give would be to make the leader long. Mine is about 20ft. that way when you set the hook, you have more stretch and you are not torquing your leader knot. Not to mention-that longer leader will be more stealthy. good luck