I've been thinking of the same subject too.
I wonder which one costs the least to maintain, the 190's are out for me. I don't have much love for them.
The 240D and 300D Turbo sound good, and so does the 300SDs..
but if the repair costs are going to be outrageous.. I'd rather spend more money on a '90 W124 or W126..
I love the W123 and as a collector's car.. I would prefer the 280E or 280CE.. if only they were easy to find..