Lino,
FWIW, I was making the same decision as you (one year ago). I wanted to buy a car for my wife to replace her aging 940 Volvo, which she absolutely loved. My criteria was (1) a luxury RWD sedan that (2) couldn't be a Ford/GM/Mopile - not sexy enough, according to my wife (3) I could do 80% of the wrenching on (maintenance) and (4) I could purchase for under $15k. My thoughts then/now on some of the models I considered:
BMW 3/5/7 series --- always loved the look of these cars. I can't say reliability ever scared me - actually, quite the opposite. For the most part, BMWs seem to run forever (driveline), althought the little things could put a hurting on you financially if you took it to an indy/dealer to handle those items. I felt with all the great Web sites / forums dedicated to this "drivers car", I would have plenty of support in troubleshooting any BMW I purchased.
Why didn't I buy a BMW? Ride is too harsh. Don't like seating position - not that comfortable to me. Don't really *care* for much of the BMW interior components. My wife would've hated it.
Lexus --- These are supposed to be super reliable cars. But, there was no way I was going to buy one - this after doing weeks of research on Lexus forums - due to the cost of parts and dealer/indy maintenance if required. And I understand, eventually --- it's required and quite painful. So, the Lexus was never a serious consideration for me.
Mercedes --- I suppose the reason I ended up getting a **94-95 W124 E320** were the ride/drive, ease of maintenance, availability of relatively cheap parts, longevity of driveline, availability of cheap unmolested (original-owner cars) and classic look --- oh yes, and great forums like these with members from around the world who drive AND know how to work on these cars. To me, the W124 is like a 940 Volvo on steroids. And that is a great thing, as owning and working on Volvo 940s is what made me really appreciate European auto engineering for the first time. Oh yes, and she loves the engine on her '95 model. Smooth, powerful and gets 26 mpg on the interstate. After owning for one year (and replacing shocks/struts, water pump, serpentine belt and tensioner components, valve cover gasket, starter motor, cabin filters, oil pressure sending unit, coolant hoses.....(I think that's it
.... and doing it myself, mostly for preventative maintenance reasons on a 10-year-old car, I have saved a fortune), I have been pleased with owning such a reliable car.
I also considered 96-98 E320s, but I felt --- and do today --- my ability to diagnose/maintain these cars would not be as great as our '95 E320. And the cost of ownership would've been higher. My wife really likes the look of the rounded headlights on these cars, though. But, she does love her '95 model.
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I think if I could go back and do anything differently, I might have considered the MB diesel models (E300) a little more seriously.
Good luck Lino! Have fun with your decision.