Hi Trevor,
I had two diesels as company cars in the nineties which I found rather good, one had the Peugeot engine and the other a Rover engine. When I retired in 1999 I had a Rover 2.5 Petrol Sterling, but three years ago went to a Jaguar 2.7 Diesel and have been very pleased with it.
But the 3.0 litre S Type has one of the best engines there is, so it is not a bad choice, but they are getting a bit rare.
Regards,
Peter.