My 2012 has been a fantastic car. It has about 50,000 miles on it now. I bought it 1 year old CPO with 25K Miles and I have not used the warranty once. The only things I have done to it was a new battery (Just last week) and oil changes, brakes and tires. Nothing out of the ordinary. I would go for the W212 because the 3.5 V6 with the 7 speed is solid and proven. The modern Diesel's tend to have issues so find a E350. The E300 is now a 4 banger with a turbo and I personally just do not trust the engine long term. Find a W212 E350 4Matic. No airmatic! I feel confident keeping my car 200,000+ Miles. Find a good MB shop instead of a dealer and get a PPI on whatever car you choose.

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2015 ML350 4Matic. Wifes DD
2015 GLK350 4Matic. My winter DD
2012 E350 4Matic. Road Trip car
2009 CLK350 Coupe Designo.Kleemann Tune For nice days/DD
2006 CL600. V12.Eurocharged Tune. Enough said
2005 CLK55 AMG Coupe.Kleemann Tune. For the sound and style
2004 CLK320 Cabriolet. 2005+ Interior swap. For the sunny Florida days & beach days