Amsterdam
by a mile.
Clean terminal, easy to find your way and a terrace to watch the planes. Only drawback is the Polderbaan, which is like a long taxi.. for those of you from the Netherlands.. I once had an EasyJet flight into Amsterdam and this was his message:
"Goodmorning Ladies and gentlemen, we have landed at Haarlem airport and we shall now commence or short drive to Amsterdam Schiphol airport."
Aside from Schiphol I'd say the new Sheremetyevo terminal. It's fantastically modern, clean and nice.