I own a 2008 528i xDrive from new and like it. I drove the BMW 535i and 3 series etc and personally believe 528i xDrive is a good choice. It is not too crazy but has plenty of power when you need it, particularly if you put it in the sports mode.
Among other cars in its class, it will be upto your personal taste and how you want to drive it as a owner. I think the MB might have a slight edge when it comes to snob appeal (at least the sales guys at the dealership seemed a little less motivated).
I participated in an event organized by BMW a couple of years ago during which we drove a MB E350, the BMW 535 and the Audi A6 on a large parking lot partitioned into a test track. A professional driver took us on the track first then we all had a chance to drive, as fast as we could, each of the three models. Of course we all concluded that the BMW was the best on that track, when we were pushing the car to our personal limits.
That said, I felt the MB E350 was pretty solid and I will probably go for it next time we shop for a new car. Maybe I am just getting old.
