Since I fish muskies with a sinking line I prefer leaders on the short side, something like this:
Butt: 2' of 40#
Middle: 2' of 20#
Tippet: 1' of 30# flouro
Bite Tippet: 6" of 20-30# wire.
You will often hear of muskie guys using very heavy line - often something like 60# braid or a straight leader of something like this. I don't like this because if you snag your fly, it becomes almost impossible to break the fly off and you risk damaging your fly line at such levels. You need a break tippet and I like 20#.