As a driver of a 430d M Sport I can tell you that I love it. I came from an F30 320d (which I also loved) but always wanted the coupe shape so this was a natural evolution.
The answer depends on your priorities so, to answer your question better, it would be good to understand what you're looking for.
In my view the 430d offers a fantastic balance of power, torque, I6 refinement and sound, economy and, as a UK company car driver, CO2/BIK tax rate. Nothing else comes close. It's dramatically quicker, remarkably quieter and way better sounding than my 320d and feels much sportier to drive. The std options list on the 4 is pretty good so you can get away without adding much. That said, adaptive suspension, adaptive lights, HK, pro nav, HUD, parking camera(s) etc all bring fantastic benefits if you use them. Even little things like folding mirrors are helpful.
Feel free to ask me any questions about the car. That said, you should enjoy a much better response to this particular question if you post it on the UK sub-forum. Do come by and say hi!
