If you go for a 201 or 124 you would likely have fewer issues with the system mechanically, but possibly more electrically, that is if the system isn't working properly when you buy the car. My 190D had great heat but the AC had some electrical issues and would work intermittently. I never quite finished track down the issue but I think it was a bad Klima relay, I replaced the push button unit because the old one had evidence of moisture getting on the board but the rebuilt one didn't change anything. I personally prefer a OM602 to the OM617 because of the more reliable AC system (among other things), as it is the same in my 190E and that works rather well.