Definitely have to echo that my two favorites are the Hotel Pulitzer in Amsterdam and W Barcelona. The Hotel Pulitzer is just lovely....great staff, wonderful restaurant, fantastic location right on the canal, great touches like heated floors in the bathrooms and is just a quintessential Amsterdam property.
The W in Barcelona is quite a distance from some of the highlights in the city, but I personally love that it's right on the beach, we have always gotten the rooms with the floor-to-ceiling views of the Mediterranean, the staff can't do enough for us and the property just epitomizes Mediterranean chic.
We liked the Westin Europa & Regina in Venice only for the phenomenal views of the Grand Canal. The hotel itself left us feeling cold and the staff isn't really very warm. But for our first time in Venice, it was perfect for the views and convenient location.