I had a Pug 306 DTurbo before I got a GT so no real comparison there except to say how much more refined the Alfa engine is than the French unit. What I can say about the GT in addition to everything said here is that it is probably one of the the most versatile cars you could own.
Looks great of course, enough power even in the standard 1.9JTD to be satisfying whilst not being so thirsty it hits you in the pocket and if you get a remap you can benefit from more horsepower, torque and better economy for not that much money. I believe the Q2 is excellent and a steal as an aftermarket add-on. I use the GT everyday on motorway and country roads and on both she is excellent, cruises superbly and then nice around the bends with sharp steering and enough torque to mean you donít have to change gear every 2 seconds like I had to in an Astra 1.6 I recently leased for a work trip.
Iíve had 5 people in it plus luggage, Iíve carried bikes in the back and no end of other stuff including a small sofa with the seats down, not sure you could do that in a 525 unless itís a Tourer.
Regarding the seats, I had the Alfatex in my first 04 GT and imo they are better than the leather I have in my current GT, they look better, are more comfortable and are more hard-wearing, plus they donít burn your bum off in summer and freeze it off in winter! As for the size of the seats, they are massive and very, very good in terms of support and comfort.
As for ICE, I had the basic 937 stereo in my first GT and it was poor in terms of sound and features, I have the BOSE now and itís 100% better but Alfaís decision to keep the standard Blaupunkt head unit and then add a BOSE subwoofer and speakers to it kind of ruins the whole thing, traffic or news updates that have a music ďbedĒ with a dull beat drive you round the twist as the sub doesnít have any controller, it sounds like someone is trying to get out of the boot. Plenty of options to upgrade the HU though and the card-tray and cup holder below the standard stereo can easily be removed and with little work you can get a double DIN unit in no problem.
Some negatives of course to provide balance Ė paint chips are a nightmare as has been said and Alfa must know this as I saw in the dealership you can buy paint protection as an aftermarket item, imo they should put that stuff on anyway. You need to get one with reverse sensors as itís like parking a postbox looking out of the back window sometimes. If you get a second hand one then the JTS needs to have had the belt and water pump done at 36K and the JTD needs to have this done as part of the sale if you can negotiate it if itís anywhere over 40K (see the sticky thread on waterpump failures) I learned the hard way and had the water pump seize and the timing belt shred at 40K, I wouldnít wish that experience on anyone. Other than that the 16v JTD engine seems pretty bulletproof and if regularly serviced it seems to get better and better with age.
As for wheels, Iíve had 17s and 18s and thereís not a massive amount of difference ride-wise imo, the car is quite sporty/stiff anyway so hitting bumps is wince-incurring in both. 18s looks great but kerbing is basically inevitable, Iím yet to see an Alfa with 18s not suffer from at least one kerb scuff. The 17s are slightly better for this as thereís more sidewall of course but try and stay away from the multispokes if you can as they are not at all easy to clean, stay well away from anything with 16s on Ė they look like castors.
Think thatís it, Iíd better do some work now!