Here's what I can tell you about transmission 722.6XX vs. 722.3/4XX. It's true, the 722.6 has had it's share of problems but it's DIY friendly. Since it has no brake bands, it's much easier, IMHO, to tear down and re-build. Any DIY'er equipped to remove and re-install the transmission should have no trouble re-building it. I also like the M104 engine. However, despite what I've read in this Forum as well as others, even the new and improved head gaskets can fail. I've seen it happen many times. My own '94 E320 had the improved head gasket installed in 1997 and I just recently replaced it due to an external coolant leak. I wouldn't let this influence the decision of which engine is more reliable though. After all, the 104 head gasket is a great DIY job. The parts are cheap and the savings in labor costs are huge! The wiring harnesses haven't been much of a problem on 210's either. I could go on forever about the pros and cons of these cars but in the end they really are great. Keep in mind though, that beginning in 1998 the 210's really became different animals. The entire vehicle is networked, meaning all accessories (windows, sunroof, seats, etc. )send and recieve signals via a databus. This is NOT very DIY friendly. Personally, my choice would be the '97 E320.