Average length of lead for me is about 30". Short leads in the 12-15" range are used on occasion when the fish are tight to the bottom.
This summer I've had to finesse them to the nth degree and my leads have averaged 6-8', sometimes as long as 12'. It might seem too long to most but believe me on pressured finicky walleye especially in clear water, that's what you've got to do sometimes.
Like Chris I rarely use a floating jig head, just a simple live bait rig with a lindy sinker and hooks of my choosing.
Many times however I'll peg a small cylindrical shaped floater within 6" of my hook...