AMS has got to be #1.
They have great stores, and even several aviation related store that sell aircraft models. Great food places aswell.
AMS is certainly a shopping mall aswell as an airport.
ATL is excelent aswell. Lots of selections is the great plus about it.
DEN is very good also. It has a Wolfgang Puck with very interesting decorations inside.
A few nice travel accessory stores aswell.
One of the worst has got to be LGW. Too expensive, nothing great aswell. Too crowded. I just didn't like it. Maybe I've been spoiled.
Anyways, just my experiences.
"Generosity is giving more than you can, and pride is taking less than you need." - Khalil Gibran