I've used and been pleased with Nikwax. They have different products. The "sponge on" or dauber type worked pretty well for leather boots and was more durable than I expected. It doesn't fill the leather like wax. The spray on type worked well on surfaces away from contact and fabric but didn't last as long on the toe section after walking through grass, brush, wet snow, etc. You might consider using wax on the front quarters and toe section with Nikwax on the less exposed part of the boot.
