My opinion may help. I have the proverbial 'Bad Egg' Alfa. The one that conforms to every Alfa Romeo stereotype. It is a MY07 1.9 JTDm Lusso in Stromboli Grey (But ordered in Black) and I have had this from new (2.5 years - 32,000miles). In this time I have had 10 courtesy cars and I find that the series 2 (MY08 to 2010) is way more refined and a good bit better than the MY07 model. You can tell the difference between them by whether the boot opens via the boot badge or not.
The Series 2 (IMHO) is sharper, quieter, more responsive lower down the rev range, and better brakes than my car (1.9 JTDm v 1.9JTDm). I prefer the dash and the dual zone climate control of the Series 1 however everything else goes in favour of the later models. The 2.4 JTDm is much better pulling you around though is noticeably heavier at the nose and definitely at the pump. At motorway speeds you notice the difference less than at pulling away from 0. A modified 1.9 JTDm would probably be best compromise. Living with the car I think that the best bit of it is the seats which I want to rip out and put into my living room. This would be my only grip against the Turismo spec cars that I have had the 'courtesy' of. I prefer the softer setup of the Lusso and Turismo spec and find that body roll is still not in any way excessive when exercising the right foot and grip is excellent on both 16" and 17" Rims. I have yet to have a Ti however in the 6 months I have left with the car there is still time. My car crashes around like a 10 year old Citroen though this has improved since I recently got the osf upper wishbone replaced. The brakes are soft in comparison to the series two which also come with Painted front calipers (nice).
Some of this may not sound positive however I do genuinely love the 159, just not mine unfortunately which I am hoping will spontaneously combust at some point - preferably without me or my family in it. And I definitely prefer driving the 159 to the 147, Mito, Insignia, Golf, Giulietta and Saab 93 when it comes to courtesy cars.
Hope this helps.