like to use 6-2 Berkley FireLine – it is more than strong enough to catch huge walleyes (or the occasional big cat). In fact I caught my largest walleye ever on 6-2 – 15.8 pounds, vertical jigging.
In the past I used Smoke colored line. I have switched over in recent years to the Berkley FireLine Crystal, especially in clear water. The Crystal is an “opaque” line that is easy to see above the water but has low visibility below the surface.