I would go for the S 320, no doubt about it!

Although, I might be strongly biased (the W140 is my favorite car, period).

But realistically, view it this way:

The S-class is top of the line: hence size, ride, comfort, features, materials quality and finishes will be far superior than for an E-class (middle weight). Case in point: just look at the side windows, which one comes with double pane?

Another issue is that the E430 was basically created for the U.S. market (mainly to satisfy the V8 crave of US owners). Hence, the E-class was really not best suited for a V8 (the engine is really cramped in there and it will give you constant heat related problems!).

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A. Rosich
CL 500, 1998
S 500 L, 1998
E 320 T, 1995 [Sadly sold ]