Just this past year team 1024 used a pair of
MA2 Absolute Rotary Encoders from US Digital on our drivetrain.
Seriously, I know everyone hears analog and thinks totally noise immune. Really, with a tiny bit of smart EMF design it wasnt a problem. However, I know personally I'd rather use a digital optical shaft encoder, but unfortunately our robot this past year was really fast and to get any kind of resolution out of the encoders the frequencies got rediculous at the top end, so much so it was impossible to track without losing counts.
So, hence the move the the MA2. The driver took just one evening to write, and works like a charm. Instead of having an interrupt in the multiples of KHz, we only had to sample the encoder at 100Hz. Best of all, you get the ability to handle a high top-end RPM without sacrificing low-end RPM positioning accuracy (our robot last year could position +/-0.05 inches at the frame).
Again, as long as you can do a decent EMF design to keep the analog signals from the encoders safe, they work like a charm. Definitely worth your time to at least research.
Questions? Post.
-q