Objectively speaking, what is/was the best diesel engine ever built?

[Wayland]

From my own experience I'd have to go with the 12v Cummins, and the old air-cooled Listers (I have 5 or so of them).

[maxfax]

My vote is for the Benz om617..   Never saw one wear out before the three bodies it's been installed in rusted in half...

[macka]

60 series detroit, or the volvo/penta in my friends fishing boat.

[dieselweasel]

I'd agree...the older Detroit 60 series (non egr) and the Cummins 5.9 (12V especially) are some damn good engines.  I'll add the Cat 3406 B, C, and E engines to the list...very common to see these with a million miles before major failure/overhaul.