For me it has to be Milan Linate, its a very busy airport for its size but there are not many shops, very little to no choice in terms of food and if you happen to be flying to London once your at the gate your stuck due to the passport control/security specifically set up which prevents you from going back to the main area of departures - not that there is a great deal to do there. All that is in the area your segregated into is a set of toilets and a drinks machine - so if you ever have the misfortune of being delayed you have had it. Ive flown a few times on a Friday night when the BA and Alitalia flights to LHR plus the Easy to LGW are all departing within a short while of each other and there are never enough seats!
The best i think ive been to is Madrid Barajas - bit of a trek to and from your gate if your flying BA and luggage can take at least 90 minutes to turn up once you arrive but the design and surroundings are perfect!