A Deutz MG 530 C from 1963, moving some specialized side-discharging wagons within the confines of the Niederaußem powerplant. This road actuall cuts right through the premises of the plant, and we were lucky enough to have the gates close right in front of us. Most people would be annoyed by that, but for railfans, it's a great unexpected photo op.
Well made hydraulic drives are generally more robust and less prone to overheating and overloading, but they don't allow individual control of each axle as is the case with modern multiphase AC engines. Plus they're less efficient than diesel-electrics, and I think top speeds are also much lower for hydraulic transmissions (which is of course not a concern for switchers).