Well I moved from a string of Alfa 156's to a BMW 120D Coupe, so it's almost comparable. I have to say I was never dissatisfied with the Alfa's on reliability, the only issues in 8 years were an electrical problem on a 156JTS and numerous suspension bushes, which I was resigned to being a service item on 156's on our crappy roads. The BMW has needed a new clutch and flywheel and has the baulkiest gearchange of any car I've owned.
Whilst I enjoyed my 156's especially the last (a GTA) the BMW definitely handles better and is way more efficient on fuel whilst being a match for the 2.0JTS on performance. It's not without it's faults though, the ride is harsh, the steering has an odd sort of feel and the throttle response is woeful.
But the main thing and this is the clincher for me, it doesn't make me WANT another BMW and I DO want to go back to Alfa, hopefully in the Guilletta I can justify that too. Would I change from a 147 to a 316?.... no, might to one with a better engine, but not the runt of the range like a 316.