I traded my 156 2.0 TS in for a JTS in March, so I have experienced both cars.
Reliability:, I think it's to early to tell really mine has been fine, but then apart from a Cambelt tensioner, so was my TS. There are reported problems with the Lamda sensor on the JTS, the wiring is fixed too close to something hot, which seems to cause it to send wrong readings, it is a simple fix, re route the wires. BTW It's not been a problem on mine.
The JTS unit isn't as characterfull as the TS, it pulls better from lower revs, but isn't quite as keen to rev as a TS, tho mine has got 13K on the clock and is starting to loosen up and go better now. Overall the performance is slightly better, as is economy, but only slightly. It doesn't sound as sweet tho, (this is reletive you understand it is still an Alfa and sounds great!) it isn't a smooth either, no balancer shafts may be the reason.
The face lifted cars (not the latest one but the last one), got a Bose unit as standard on the 2.0 and above, so the sound is definatly better, my radio reception is OK, but I have had loan cars which were crap, so look out for this, and complain to the dealer if necessery.
The dual control AC is clever but I don't think it is a vast improvement over the old one, I had a fault on a Car which I rejected after a fortnight because it was underspec, the AC on that Car just didn't work properly. The one on my car is fine now, but it is complicated to use, best thing to do is set it how you want and leave well alone. If you fiddle with it, it tends to get confused. (Well... perhaps it's me
Other things to watch for are, short spec Cars, a number of UK supplied Veloce's had things missing, ie, no Electric windows in the back, and no Headlamp washers, these should be a bit cheaper, this is why I rejected mine and got a replacement.
Insurance on the JTS is up two groups on the TS, which makes it as expensive as a V6, this is a bit anoying considering it isn't much faster than a TS. If you don't do many miles and Economy isn't an issue, think about a V6, if you do a lot of miles think about a JTD, it's as fast but more economic and cheaper to insure.
I still like the JTS and it is a good compromise, they handle better than the V6, and JTD, being lighter at the front, should be some bargains about at the moment as well. Good hunting and keep us posted.