I own both, but the driving experience is with the W140, but I understand you do not DIY much, so the W210 is a "Gas-up and go car" Personally, in your circumstances, i would do the trade on a 2000 to 2002 as it has the updated transmission, and more airbags.

If you are a big wide guy,the W210 will feel a little cramped

97 to 99 you have to worry about the Transmission K2 bearing failure(the whine sound), and the rust on the front spring perch for the front....Get a non 4matic if you can..

W140 S500 versus W210 E320... looking for advice - Mercedes-Benz Forum

MArtin