Hyd discs are fantastic. What are they like covered in mud? Great. Ask a MTBer what the best development is in the last 10 years. They stay cleaner than rims because they are generally out of the mud, and they work, wet or dry. Ask a motorcyclist. Better yet, you don't wear your rims out. My original MTB would chew through brake pads in a wet afternoon or two, and rims in a couple of seasons. My disc equipped MTBs brake pads last most of a season, the discs seem to last indefinitely.
The only disadvantage is a weight penalty, so no thanks for a roadie, but as soon as you go off road it's no contest whatsoever.