I have had my 159 TI SW for 3 months, previous to this i had a GTV Twin Spark and still have a 156 2.4 JTD.
I guess its a natural progression to go from a 156 to a 159 and here are my thoughts if anyone is interested lol
The 2.4 10V in the 156 is a peach of an engine, fast and a great sound for a diesel. Had her 4 years and no issues in that department. I was not amazed by the 1.9 in the TI to start but i must say its much better now i have put some fuel cleaner and Performance Fuel in it and done a few thousand miles.
It does have a nice amount of power and it does shift in 3rd and 4th just a bit slow off the mark due to its weight i guess
The build quality and comfort in the 159 is a different league and its a very nice place to be. Handling wise i would say there isn't much in it. The 156 is slightly more direct in steering but that's about it.
I did a 500 mile trip to Liverpool in the 159 a few weeks ago and averaged 46mpg, around town and to work and back it does 37 ish.
TI Seats are lovely but have a weird fault with little threads coming out in places. I had a puncture a few weeks ago on business, £210 later new tyre fitted
Gearbox on the 159 is notchy, no weird noises (thank god) but notchy compared to the 156. The 156 box is smooth and feels more solid in general but its a bit like stirring porridge lol
159 Brakes are decent, but never had any issues with the 156 brakes there also good.
Looks wise the 159 in my opinion is the best looking estate on the road so im more than happy with that!
With a remap i think the 159 will be pretty much perfect for what i need.