2004 BMW 3 Series 325i Rwd 4dr Sedan (2.5L 6cyl 5M)
I bought my car from its first owner in Sept. 2010, and the only regret that I have had is that I did not buy it sooner. I'm a first time BMW owner, and I now know what they mean by the Ultimate Driving Machine. With the 6-speed, the car is more than quick enough to maneuver through traffic. For some terrible reason, this car becomes even more fun as the speeds climb. At 100+ MPH it still feels like it's on rails. Mechanically this car seems immaculate, I love the perfect mechanical sound the gear box maxes as you change a gear at low speeds. Both exterior and interior build quality is fantastic; and I love the driving position/feel despite being 6'2" and 225 lbs.
The inline 6, handling, transmission, and build quality.
None (maybe just the ability to make cars in front of you disappear!)