I had a 2007 E92 335i as a lease. It was a great car, they replaced the fuel pump once (before it actually failed.) No problems otherwise when turned in at 45K and 3 years. We ended up ordering a 2009 G37S Coupe to replace it after much debate. The idea was that I would drive the G37 for about a year and then give it to my wife for her daily driver and order myself another 3-series. As mentioned above (by those who have actually owned both), the G37 is probably 9/10s of the BMW in performance and driving feel. The steering is definitely numb, but it handles quite well once you get used to it. Both of mine were autos, and the G's rev-matching downshifts are really impressive on a curvy road. The interior is not as nice, but the electronics are at least a generation better than the 3. The nav is the best I have ever used in an OEM setup. Trunk is tiny, but seats fold down flat to make up for that somewhat.
After test driving the new Audi S4, I decided to go that route instead of another 3. It is a very impressive car, especially with the sport diff. Handling is much better than the 335xi that I was comparing it with. The power is at least on par with the 3, maybe slightly better even. You feel the weight in the corners, but it still sticks like glue. So, within the span of about 15 months, I will have owned the 335, G37, and S4. Honestly, I would be very happy with any of the three.