I just ordered a set of Bilstein HDs for my '97 S420. Most of the posts I have read on the subject favor them because of their OEM ride quality but better control. I haven't put them on yet, but I hope to do so this week. Most also agree to stay away from the Monroes. YMMV, of course.

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"It's not about how fast you can go, but how well you can go fast."

Bob in Richmond

'97 S320 (LWB), Ruby Red Metallic, 73k miles
'97 S420V, Smoke Silver Metallic, 155k miles