[kazinator]

The better ones are delrin (a.k.a acteal). It has a low coefficient of friction.

[OJFord]

Interesting, thanks, I probably can't tell the difference and have just assumed they're all nylon to be honest!

[sudosysgen]

Delrin gears are not uniformly better. They have a lower coefficient of friction, but they can handle less torque. It's a tradeoff.