Value means different things to different people, but if it is reliability that you want, you are sipping at the wrong well with either MB or BMW. You want reliability in the higher-priced brands, you want a Lexus or Infiniti or Acura.
I have a 1992 LS400 that I have owned since 1993 in Michigan (know for crummy roads). It is, by far, the most reliable car I have ever owned. Give you an example, this car had an in-service date of late 1991, so it is almost 19 years old. In those 19 years the only lamps that have been replaced on the car are its parking lamps (2 bulbs). All other lighting still works and is original. There have been zero powertrain issues (engine/transmission/axle). The shocks are original and work fine. Brakes have been re-done twice (new rotors once). The exhaust system is original and works great.
Last fall I had to have the brake lines replaced because of corrosion (the car is driven daily in winter in MI where lots of salt is used). I, foolishly, did not have the car under-coated every few years and Toyota did not use stainless brake lines. There was an elusive electrical ground problem (corrosion caused) two years ago. I replaced the HVAC dash control with a rebuilt a few years back when it started to partially fade out (a common problem with Gen 1 LS400's).
That's it...and a few battery replacements.
I now also own a 2006 E320 CDI bought last year. If that car proves 1/2 as reliable as that old LS400, I will consider it a minor miracle given what I see in CR owner reliability ratings. (I bought it for the diesel engine...if Lexus had a diesel model, I would have bought it in a heart-beat instead.)
When people talk about Mercs and BMWs and good reliability, it always makes me wonder what they have in mind given the historically rather poor ratings in CR owners' survey. They do seem to be getting better...at least on certain models.
I decided to change over from a Beemer to the Merc, really for its value and dependability.
Yes, I will miss the 'Driving Dynamics' (or whatever latest buzzword Munich uses now :-D) of the Beemer, but I strongly believe that 'a well maintained old Benz' will produce much fewer problems, and be less costly to maintain in the long run.
Well - that's the theory - let's see how things turn out!