Agree 100% with what has already been said above.

Being a die-hard w123 and w124 fan, I was at first very skeptical of the w210 cars... but I've been "converted" to a large extent. In addition to my w124's, I've got both a w210 gas sedan and a 4-matic wagon, plus a '98 E300 turbodiesel. (I particularly *LOVE* that wagon, even though I describe it as looking like a Hearse.)

The w210's are pretty easy to diagnose and work on, although after you first get things dialed in, you won't be needing to do that very often. Please know that they do drive very differently than the w124's, and the w210's do have a few common idiosyncrasies. Once those items are addressed, they really are very, very reliable. The M112 engine internals are bulletproof. A local well-known MBZ mechanic once said he has never ever had the heads off of an M112. The valve cover breathers eventually leak but are an easy fix. Spark plugs are good for 100,000 miles. The 606 engines in the diesels are legendary for their robustness and reliability. The 722.6 transmissions did have a revision during the production run to address an internal bushing that sometimes caused problems, but if fluid changes have been done on a regular basis, then the only thing to go wrong is the electrical connector/bushing ($15?) or the conductor plate. I'd go with a facelift version w210 for the upgraded trans, but there are other perks with the facelift versions too.

For the gassers, in addition to the usual 'new' old car prep of a new belt, hoses, and fluids, I'd suggest replacing the crank position sensor as a cheap preventative measure. Expect the window regulators to fail at some point if they haven't already been replaced. I drive long distances, so I went into overkill by doing the trans conductor plates and electrical plugs while I was already changing the fluid. I also bought a MAF sensor that I take with me on road trips along with a K40 relay... just in case. Oh, almost forgot to mention keeping the front wheel bearings packed, as I've read they seem to be a little more prone to failure compared to earlier chassis's.

__________________
Current rolling stock:
2001 E55 183,000+ Newest member of the fleet.
2002 E320 83,000 - The "cream-puff"!
1992 500E 217,000+
1995 E300D 412,000+
1998 E300D 155,000+
2001 E320 227,000+
2001 E320 Wagon, 177,000+

Prior MBZ’s:
1952 220 Cab A
1966 300SE
1971 280SE
1973 350SLC (euro)
1980 450SLC
1980 450SLC (#2)
1978 450SLC 5.0
1984 300D ~243,000 & fondly remembered
1993 500E - sorely missed.
1975 VW Scirocco w/ slightly de-tuned Super-Vee engine - Sold after 30+ years.