I'm sure the Konis are good too. Perhaps I 'travel' in different vendor circles, but I have not even seen Konis listed for a 124.
If they are the type that can be adjusted post-install with a knob, that is a pretty cool feature, but I recall them to be fairly expensive.

I really like the HDs. They are firm, but not harsh, and work very well with stock springs. They perform surprisingly well under a wide variety of road and speed conditions. You get somewhat firmer damping without spring or other suspension mods, which is a good deal. As Steve said, they may not reduce the 'net lean' in a turn, but they do manage lateral transitions more effectively.
I am not interested in a lower ride height or stiff springs for daily driving on frost-heaved/pot-holled roads. I have used HDs on 3 different BMWs, 1 Audi, and my current 124. Never had a single complaint or failure.

I have stock size wheels and tires on the 124.

I had one good Koni experience on a BMW, and one poor Koni experience on a Honda. On the Honda, they were simply not in sync with the stock suspension. These Konis were adjustable, but not post-install.

Happy trails.

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1986 300E 5-Speed 240k mi.