My vote is the 87, but I'm a bit biased. The turbo 603 pulls very strong at any rpm and speed. It is also from the simpler to work on era if you turn your own wrench. The only thing computer controlled is the idle.

The 606 has such technical gizmos as variable length intake runners and other trickery to get near turbo performance and better fuel economy, but at a cost of not so simple to work on.

You see both on ebay with over 350,000 miles with regularity so the longevity is what one would expect from a benz.

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1959 Gravely LI, 1963 Gravely L8, 1973 Gravely C12
1982 380SL
1978 450 SEL 6.9 euro restoration at 63% and climbing
1987 300 D
2005 CDI European Delivery
2006 CDI Handed down to daughter
2007 GL CDI. Wifes