Cycling. (Diesel hydraulic used higher revving diesel engines, but were a LOT more powerful for their size. Hence a small 8 wheel diesl hydraulic loco would outpull a larger 12 or 16 wheel diesel electric.
The only reason why here in the UK they moved to a diesel elwctric policy was that Brush... Who supplied the traction motors had big connections with certain MP's who happened to be shaeholders...
In reality, though due to the higher revving diesel hydraulics needing to be serviced sligtly more often, this did not mean that the diesel electrics had the advantage... Mainly because a diesel hydraulic had a far better performance. An example of this was when a driver told me how he pulled a 16 coach train using a class 35 diesel hydraulic (Known as a Hymek) from Paddington towards Walss, and during the entire service he disn't lose a second of time. He said if he tried that with a diesel electric like a class 47 (Which was larger) he would have needed to double head and used two of them to keep to the timetable times with such a heavy train.
Tank engine or a tender engine?