I think either one if well sorted would be a nice car to own. I have both a 190D 2.5 automatic and a 240D manual but have only driven the 190D. It rides very well and though I have no idea about if any major engine work has been done, the engine at 315,000 miles runs very well and I feel it has enough power. The automatic transmission was replaced with a remanufactured one as one of the first things when I bought the car and I think it is a very good transmission. The downshift button used in Mercedes with automatics is probably one of my favorite things to use. You are getting up to a hill and push the throttle all the way forward, click the button and the transmission will almost instantly downshift. I wish all cars with automatic transmission had that, I get tired going up a hill and having to wait 5 seconds for the transmission to figure out it needs to downshift in the fords we own. It isn't fast but I feel it has enough power for highway driving, though you may not be able to keep going as fast as you want to on a grade. I have gotten around 37 mpg driving 70 mph on a trip from Florida to Georgia. I can't really say there is any reason why you must buy a 240D over a 190D unless you need a manual transmission or like the look of the W123 more. Either car will be nice The W123 has less complex and slightly cheaper to replace suspension components but the prices for W201 suspension parts are not too bad, especially here on Pelican Parts, and I think overall, parts for the W201 are more readily available than the W123. The OM602 should last you a long time as long as you keep it from overheating, perform the obvious regular maintenance, and have the updated vacuum pump.It is more complex than the OM616 but definitely not that hard to work on. The OM602 is a bit more refined. The W201 is also nice to drive in the city because its turning circle is so small. Also a huge advantage to me of the W201 is the opportunity to upgrade to the 1990 and later seats, they are much more comfortable than the original W201 seats and probably the W123's seats.

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Current: 1975 450SEL, 83 300D, 88 Yugo GVX, 90 300D OM603 swap, 91 F150 4.6 4v swap, 93 190E Sportline LE 3.0L M104 swap, 93 190E Sportline LE Megasquirt, 03 Sprinter, 06 E500 4Matic wagon.