I had a Stilo too, the 5-cylinder did sound really nice, I agree.
The V6 in my 164(s) sounds fantastic so I can agree with the people saying the V6 is the best choice.
But I like the sound of the 2L Twin Spark too. It reminds me of the FIAT Coupe (which, like the TS, had balancer shafts). It's a purposeful growl - much more pleasant than the thrashy sound of the Punto I'm replacing. I've avoided taking the TS over 4,000RPM, due to the cambelt being way overdue... it's more or less parked up till I can do the job in December.
I think we're a bit spoiled, us Italian car drivers, as all our engines sound nice (though the FIAT 1.2 16v is a bit disappointing, most FIATs going back through the years sounded pretty good (Tipo Sedici springs to mind, basically the same as a Coupe), and I doubt that Ferrari or Lamborghini have ever made engines that didn't sound nice (having said that, I was a bit disappointed by the flat four-cylinder noise of a 430 being driven in town...)
I wonder what a diesel Alfa sounds like... never seen one in NZ