Either place the BMW will serve you well. I have a neigbor that has an Infinity FX and a BMW X3. When I was looking to get an SUV, I talked to him about his and while he liked the FX, he wished he would have gotten the X5 for himself as he loves driving his wifes X3. But he didn't wanna be a "double beamer owner" LOL! He said it was like going camping with a good pair of sneakers. You know you should have boots, but tenny shoes just do everything so darn well. It was actually our talk that helped convince me to get the MB. He took a few extra steps to let me know that he's had the X3 almost a year longer than the FX, while the X3 has never been in the shop, and has only had 1 oil change so far, ( it had 19,000 miles on it and he said he has had it just over two years.) and the FX has been in the shop 3 times, and has cost him more in regular maintenance then the X3.
I know there are Toyota'a and Honda's that have been known to go a lifetime without issue. But I've owned Fords and Chevy's that have acheived the same, and I know of some Beamers and MB's that have gone just as long as well. If I'm not mistaken, a European car holds the record for the most miles on the original engine and drivetrain. I'm pretty sure it's a 40 year old Volvo P1800 which last I heard just turned 2.5 million miles! And it's been privately owned the entire time! So just get what you like.
*** I found an article about that Volvo.....
http://www.theautochannel.com/news/2006/06/20/011973.html