For freshwater artlure, 30lb test braid (Berkley Whiplash or Spiderwire) on spinning reels with a mono (Double XX dull green) leader of around 0.30mm diameter works well for me ... On my baitcasting (revolving spool) reels, 50lb test braid with (usually) a 0.40mm diameter leader ... The leader diameter/ strength may be adjusted up or down according to species tageteted and conditions. So, too, you may adjust the mono leader length. I use from 1m - 5m of mono leader.
Most fluorocarbons, in my opinion, could be overrated and do not hold a knot as well as mono. I have used Berkley Vanish (the older Vanish) some years ago and I was NOT impressed at all - it had a habit of failing/ breaking for no reason at all. Seaguar fluorocarbon leader material is good, but very expensive (and has a rather thick diameter relative to test poundage), but I could not fault it. Just remember that fluorocarbon takes MUCH longer than mono to degrade. Mono is not enivronmentally friendly, but fluoro is MUCH LESS environmentally friendly than mono ... I will, generally, just go with Double XX dull green mono for my leader - it is tough, supple, abrasion resistant, holds a knot really well and does not seem to bother the fish - what more can you ask for?
A further advantage is that the braid seems to last just about indefinitely (about 6 years for me now ...) and all you have to do is periodically refresh your short piece of mono leader. Much kinder to the environment as well! Also, you will probably never lose a fish due to line breakage or not having enough line on your reel. If you do have to break off after hooking up on the bottom or structure, the line will break at or close to the knot usually on the mono leader, leaving less junk in the water.
