I changed from a 3dr Stilo dynamic 1.6my 2.0 selespeed 147 and have not looked back since.
Performance, unbelievably better, even before my remap, low down punch to top end the alfa trounces the Stilo, its feels revier, lighter and more responsive, though the Stilo 1.6 was known to be a slouch. The 2.0 Alfa you will enjoy. Get it remapped, it will move like a train! Also, if you can, a BMC induction kit. Extra peformance for little money, and a nice sound.
Handling, the 147 feels like it is glued to the road, and lowered it feels even better. The Stilo although solid, felt as though the rear was falling out of the corner when pushed.
Style, well the 3dr Stilo was not bad looking at all, in fact, I really liked it. However the 147 is simply gorgeous, especially lowered and with the supersport alloys I have.
Reliability - well, they are both hit and miss, but the Alfa in my experience has faired much better, everything went wrong with my Stilo.
As for the interior, the Stilo was better than most Fiats before it but still pretty rubbish, shiney plastics on the console and gaps in the fittings. The Alfa is a sexy well put together interior and uniquely styled and is timeless. The stilo is a inferior german replica.
Dont get me wrong I enjoyed the Stilo when it worked, but it really does compare to an Alfa 147 in any department. The price premium is there and its there for a reason, you get what you pay for.
For comparison, here are my cars, the old Stilo and my current Alfa.
Hope this helps.
Enjoy it, you will not look back. The 147 is a peach!