I told my colleagues that I'm thinking of getting an X3. All of them immediately told me not to citing examples of 3 people we know that had lots of problem with their Bimmers in general and the number of times they had to bring them in for service. I'm really spooked so I'm actually considering the Mercedes ML350. What do you guys think?

Well, the ML 350 is not in the same class as the X3, so that is one issue. I would go with the BMW. Either you are a Bimmer person or you are not. It's as simple as that.