W211/W203 with M112/M113 engines and 722.6 transmission are by far the cheapest and easiest MBs to DIY maintain. W210 would also fall into that category if diagnostics wasn't such a cluster****.

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CENSORED due to not family friendly words

Iv'e owned a W124 (sold w/ 236k), and now have 2 W210s (sedan with 175k and wagon with 205k). I would agree with the W210 recommendations. Go for a facelift 2000-02 or 03 for the wagon). Also look for transmission service and no rust. There are nice examples for little money.
For some issues you need the MB software to fix them. It also makes it easy to troubleshoot. Any good independent mechanic has one or they can be purchased by individuals and are relatively inexpensive. They also work for many other models. I only recall using the software twice for both of my W210s. Once to clear limp home mode when I spilled coffee on the shifter and once to identify a faulty sensor (out of dozens of possibilities).

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07 E350 4Matic wagon, 06 S430 4Matic, 99 SLK 230
retired W210 (x3), W124, W126

Thank you all for your replies! Real life intruded, so it has taken me a while to return to this topic.

The responses were a bit of a surprise. I anticipate replacing my W124 -- maybe! -- as it approaches 40 years old. I had expected some enthusiasm for models newer than the W210. Other than general comments on the usefulness of some of the newer technologies on safety and diagnostics, I found none. As I say, surprising.

I'll keep plugging with the W124, and see how long it lasts as a reliable daily driver. I don't drive that much, so it might be quite a while yet. And I will keep the recommendations here in mind.