Hi Mate
I am a huge diesel fan, been driving them for years. Love the easy going nature of them. I however always had a performance petrol car on the side for a bit of a blast.
I personally went for the 320i recently as I couldn't justify a 6 year payback for a diesel. I do enjoy the way she drives. Nice and easy when you want, but very lively when you need it. There is something to be said about revving above 4000 rpm........
As for economy, it's totally dependent on your right foot. If I wind it, I will get around 12l/100km, but driving at the speed limit down to Durban, I managed 6l/100km and 6.7l/100km on the way back. In 85% town driving, I managed just over 10l/100km recently and that was all short trips of about 3km, never really allowing the car to warm up completely. Put that in perspective, my wife's Jetta TFSi DSG, which has the same type and size of engine, used 8.2l/100km on the run down to Durban this past Sunday and am averaging around 13.4l/100km on the same sort trips.
At the end of day, it's a very personal choice, we can all tell you our views, but only you can make up your mind.