I have owned a 98 E320 (V6 engine) for the past 1 1/2 years with no major problems. I also do all of my maintenance myself. The filters are pricey but last longer than my non-Mercedes cars and the engine holds 8 1/2 qts. of synthetic oil.
I believe that the 96 model has the straight 6 with a 4 speed transmission. The 97 model has the straight 6 with the electronic 5 speed transmission. The 98 model and above has the V6 with the electronic 5 speed transmission.
With the help of Mercedes Shop, Fast Lane, and the wealth of advice from its members, you can't go wrong with any Mercedes vehicle.
1998 Mercedes E320, 200K Miles
2001 Acura 3.2TL, 178K Miles
1992 Chevy Astro, 205K Miles