For the US, I'll say NYC because we do not have to fly.
For Europe, I'll say Barcelona as it is the actual port unlike other advertised cities such as Rome. Also, our first cruise was in the summer of 2002 to celebrate our wedding anniversary. Firsts are always memborable, plus as the travel industry was still recovering from the horror of 9/11 the cruise line (Royal Caribbean) gave all who bought transfers a free tour of the city on the way to the ship. And the Gaudi architecture is truly memorable!