I will be returning to BMW in the next couple of months after having made the mistake of leasing another vehicle which was not a BMWand regretting it every day I drove it so I need some insight. I am going to purchase pre-owned because I cannot afford a new BMW but I am looking at either a 335, 535 or M. Question is, based upon owners experiences, would it be worth it to purchase an M over the 335 or 535 in regard to upkeep and future maintenance? I realize I would have to purchase an M slightly older then either the 335 or 535 and also the M does not come in an All-Wheel model. Would appreciate all the help I can get. Thanks.