I agree with everything above, apart from what JTS does. What it does is up to about 1750rpm it uses direct injection technology to fuel the car, thereafter it uses standard injectors in the inlet manifold. This is supposed to reduce fuel consumption. Its like what VW/Audi, Honda, Mitsubishi use except that the change over to ordinary injectors happens much later with these models (about 3000rpm).
I would agree with the diesel sentiment wholeheartedly: I've had a 1.9 petrol and diesel and the diesel really suits the car. The petrol - particularly on short journeys likes a drink!
Remember too that the 1.8 is not an Alfa engine and is not related to any other 1.8 engine in the Alfa range. In vectras it is considered weak and thirsty - in order to obtain performance it is low geared - about the same as a 1.6 147 ie 4000rpm at 70mph. It is also the only 159 with a 5 speed gearbox - (it came with the engine!) although in some respects this is better than the 6 speed in the rest of the range.
My only advice would be to test drive both for as long as you can doing what you would normally do.....and then feedback here!!!!
146 1.6TS, 156 2.0TS, 156 1.8TS, 147 1.6TS, 147 2.0TS, 159 1.9JTS, 147 1.6TS, 159 1.9JTDm, Mito 1.4, GT, Giulietta 2.0JTDm, Giulietta 1.4tb, Giulietta 1.6JTDm........