Not a whole lot of difference. the big one is starting in '98 it is the V-6 engine. Very smooth however they require synthetic oil. Some engine problems with the 98/99 models when MB did not use it in the first two years, but mine is fine. (I bought it from my daughter and knew the history, otherwise I would be super cautious about these years.)
It has a variable ratio steering which is really nice, a newer model radio, an electronic key system, couple other small goodies.
Same transmission as the '97. This transmission came out on the S-420 in '96 and the E-320 in '97.
Prior to buying this, I had a '94 wagon and had planned on keeping it, but my daughter made me an offer I couldn't refuse. I do like it better than the '94 except for the body style, but that is personal preference.
Whatever you get, get the service history, if it is available, be skeptical. A private owner should have it. An MB dealer can print out everything they have from their computer.
Ed

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Ed
1960 220 SE Coupe (Ponton)
1999 E320 Wagon
2007 E350