Test drive both before you decide. The W211 is a much more modern car in terms of amenities and handling but the interior is smaller and some repairs will be more expensive. Diagnostics on the W211 are much easier and cheaper to DIY than the W210 so thats a big plus for me. I think its down to personal preference and what you can find in your local market. I have a W210 diesel and I was shopping for a W211 wagon before I ended up buying a W203 wagon. I wouldn't even consider buying a W203 until I drove one.

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CENSORED due to not family friendly words