We had a chance to test drive our BMW 325i test cars with both lowering springs and coilover shock/springs installed and what an experience!
The cars outfitted with the O.E. shocks/struts and the Eibach Pro-Kit Springs ("mild" lowering, about one inch of drop) felt nearly as comfortable as stock, but helped the car feel more responsive to steering input.
The Eibach Pro-System Plus Kit "sport" springs lowered the car nearly two inches and made a noticeable change in both handling and ride comfort. It was nothing that I felt was too stiff for daily use.
The Eibach Multi-Pro Coil-Over R1 Kit was set up to lower the car about two inches as well, but the more aggressive shocks made a pronounced change and took a fair amount of comfort out of the ride on city streets and highway runs.
While the coil-over gives you the flexibilty to adjust your ride height to make it "just right," it will come at the cost of some ride comfort. I'd say that coil-overs are best on a track car in my opinion!