I've put leather covers on several wheels, and have always used waxed nylon or dacron whipping twine. It has outlasted the leather in all cases.
While the Goretex or Tenara are great materials, but are VERY slippery. This means that if your wheel
stitching comes loose anywhere it will loosen clear around the wheel. Frankly, it doesn't seem worth the trouble and expense to use these high tech materials in this application. For covers and the like it is really great, though. Our boom bag is now almost nine years old and the Tenara stitching is still intact and good looking. Many canvas
workers won't use it though, for its slipperyness makes it difficult to get stitch tension consistently correct.