I love my 87 - great car and low maintenance costs. The m103 engines had a reputation for valve guide issues and leaks at the timing chain cover, but the late m104 had a reputation for head gasket problems. My tech says he prefers the m103 to the m104, and I believe some others have said the same thing on this forum. All the w124 bodies have similar issues regarding the AC. The earlier w124s were lighter and faster than the later ones, but the later ones had a bit better gas mileage. All had the same rock solid body, but the later ones added extra goodies like dual air bags, front door speakers, 8 hole wheels which were easier to clean, etc. The early ones could be had with MB Tex vinyl interior, which I have, and prefer to leather (looks identical, wears better).
There are quite a few threads in the archives on buying a 300E, relative performance between years, Sportline suspension option, stereo upgrades, etc. A search would be worth the effort. I would take the best condition and records documentation regardless of year. If you find one that has already had the evaporator coil replaced, so much the better.
2003 Firemist Red/grey leather SL 500
2015 Palladium Silver/black mbtex GLK 350
1987 Smoke Silver/burgundy mbtex 300E Sportline (SOLD)
Click to see 87 300E