This is my first BMW. I have driven 3,000 miles since purchase and have been impressed by build quality and technology. I was drawn to the X5 by its looks, both external and internal, and BMW Ultimate Service. I opted for 3.0 over 4.8 due to significant addtional cost of the V8 and a little better fuel economy. I also own a Mercedes GL450 which I prefer over the X5 if you really need or want a V8 SUV with a useable 3rd row for kids or for towing.
BMW has the edge over Mercedes in technology department. The iDrive with Technology Package is terrific.
Seats... having trouble getting a comfortable postion set. In hindsight, I guess I would spend extra $ to get the Comfort seat option.