Middle of the model run
I would suggest the middle of the model run. Experiences of other club members here (and my own) suggest the earlier W124s are actually more reliable, especially considering they have covered greater distances. The later M104 (2.8 & 3.2) powered versions give the most trouble here. My father's '93 E320 coupe is no exception. With only about 130,000km it has been more troublesome than our '90 300TE with 175,000km (and more difficult to work on). Friends with earlier versions (late '80s) have had even less trouble. I much prefer the appearance of the late '89 update over the early models and (like Paul S) even prefer it to the '93 update. I like the ease of working on the M103 and its quiet, smooth, unfussed nature. The 3.0-24 M104 does have a potent top end though and the 3.2 M104 adds useful torque (as well as more noise). I cannot comment on V8 versions as we got only fours and sixes in Australia. Locally, the fours are accepted as offering the best handling with less weight out front. Unfortunately, they come up a bit short on power and aren't as smooth as the sixes. If outright power is not of greatest importance then my vote is for a '90 to '92 with an M103 (3 litre).
107.023: 350SLC, 3-speed auto, icon gold, parchment MBtex (sold 2012 after 29 years ownership).
107.026: 500SLC, 4-speed auto, thistle green, green velour.
124.090: 300TE, 4-speed auto, arctic white, cream-beige MBtex.
201.028: 190E 2.3 Sportline, 5-speed manual, arctic white, blue leather.
201.028: 190E 2.3, 4-speed auto, blue-black, grey MBtex.
201.034: 190E 2.3-16, 5-speed manual, blue-black, black leather.