Rigging for what kind of models?
I've had excellent results with tippet line. It comes in some very fine gauges and it's very stretchy material. I use it on any aircraft that need it, whether WWI rigging lines or WWII antennae etc. Usually it's green or brown and sort of transparent. It's probably invisible under water, which makes it so good for fly fishing. So I drag the line under a Sharpie (permanent ink marker) using either black or silver.
As for sizes, the finest I've seen is .001" (it resembles human hair) which I have used in 1/72 WWI biplanes. Usually I use .003" stuff for
1/48 biplanes and any airplane antennae. With 1930's aircraft rigging, you have to be careful since tippet line has a round cross-section; those planes used airfoil shaped wire. It's flattened. There's another product which I have, but haven't used yet, called EZ-line which I ordered from bobes hobby house. It's rubber and had a flat profile. That will work great for those 1/48 1930's biplanes.
Sewing monofilament is not nearly the quality that tippet line is, and I can't comment on EZ-line until I've actually tried it. It has an accurate cross-section that is difficult to find in any wires or lines out there.
--- Stephen