[nickbrickmaster]

Quadrature encoders are the standard for drivetrains.

Andymark has USDigital E4T encoders, which work well with their gearboxes. I have had bad experiences with their connectors though. They also sell SRX magnetic encoders, which we got this season. They require additional machining, but seem better in most other ways. Many teams also use Grayhill shaft encoders (you can find them on Digikey), but you will have to find someone else to talk about these.