if you're looking to buy a brand new car (which i'm assuming you are), BMW has the best overall warranty coverage of all the companies we're talking about. For example, BMW, unlike Mercedes, will cover your brake pads/rotor changes FOR FREE while you're under warranty. They usually have excellent service.
Mercedes has a pretty comprehensive warranty program as well, minus the brake-wear. The old ML (especially the ML500) had serious brake pad-wear issues - but from what I hear that's pretty much all been taken care of with this new model.