Most of my travelling is done within Europe. The major UK airports just don't figure - slow baggage reclaim, too much shopping, not enough seating - and then there the B****y farce which is UK immigration controls.
I would nominate AMS as the best major in Europe - everything in one building, the excellent rail connections, and space to move in amongst the confounded retail outlets.
Of regional airports, I would nominate Nürnberg. It well designed, and extremely efficient, and again, not overly contaminated with pointless shops (who - for heavens sake, needs to buy a matching set of luggage when they leave an airport. Surely most PAX pack before they get there!).