I have a Euro '97 E300Turbodiesel chipped to 200bhp+ and I can only descride it as a Sledgehammer. Have previously had an '81 300D W123 Euro 5cyl. Very frugal, very strong. Sold it with 275k miles. Then a '91 300D W124 Euro 6cyl. A lot thirstier, very quick, very reliable. Sold it with 175k. Choice entirely depends on budget, economy expectations and desire for speed. You are certain to enjoy which ever Benz you buy. In germany today you can have the S400CDI with 245bhp and I'm sure Brabus etc can improve on that. I even hear talk of an AMG version coming soon.
'97 E300Turbodiesel "Superchip" 200+bhp
'00 A140 Avantgarde Auto
'91 500SEL W126
'66 220SEb Coupe (restoration pending)
'58 180D (restoration underway)