The perfect fluorocarbon leader for walleye is as invisible as possible underwater and has a 10-12lb test. When lure fishing, you will want to use a somewhat stiffer leader material. When fishing with smaller live baits, your leader should instead be softer and have a little stretch to it.
For walleye per se, you do not need to use a steel leader at all, as they won’t be able to bite through your mainline. However, if the water you are fishing in contains pike or muskies, you can use a 10-15lb fluorocarbon leader instead of steel, in order to prevent bite-offs.