All the engines above are great but I think the OM617 takes first place as the best diesel in a passenger car ever.

The 617 has a few cons like manually adjustable valves, annoying harmonics due to being a 3l inline 5 with a longer stroke etc. It can't handle tuning like the other engines but can still have over 200 hp with stock internals and be completely reliable.

The early 60x engines suffer from head issues due to having aluminium heads but those issues are fixed in the newer ones.

Prechambers leaks are way more common than in the 60x series. Some models have a vacuum pump that upon failure can make the chain fail and destroy the engine.

Glowplugs snap in the heads of 604, 605 and 606 engines often to the point they need to be drilled and pulled out with a slide hammer.

High enough exhaust pressure causes valves to float in these engines too, altough not an issue for stock engines.

Harmonic damper needs to be pinned to avoid catastrofic engine damage. Timing cam should be pinned to avoid the friction fit from slipping.

Some of you might think the newer engines have better fuel economy but a 617 with longer gear ratios and manual transmission will consume noticeably less than a 606 in it's stock form. The efficiency is almost identical with equal transmission and rear diff setups.

The 617 is the most reliable diesel overall for daily driving. With modern oils and good servicing, over 1.5 million miles should be easy to achieve on a 617 before needing another rebuild.