It depend on what kind of ride you want. The Sport setup will give you more of a road feel, that genuine "BMW" ride. However, it is a bit rougher over bumps and potholes, so you have to be careful. I don't have the Sport on my 4.4i and although my truck won't corner as well, it is a very respectable ride. I'm actually pulling on cars in turns with no problems, and those soccer moms in their Pathfinders have to slow down at the curves.

The comfort and sport seats are both very comfortable, but IMO the sport seats do become a bit "stiff" after a long ride (4-5 hrs+). The sport seats are meant to bolster you in during driving and turning, so by nature they have less cushy material. Whatever choice you go with, it wont be wrong.