I've sailed on the Century, the Mercury, and the Millennium.
I preferred the looks and layout of the Millennium in most cases. The exception... I think the Grand Restaurant on Century is one of the most beautiful dining rooms at sea. Mercury's and Millennium's didn't live up to that in my view.
However I think Millennium generally had a very "distinct feel to her", whereas the Century class have more of an "every other ship" feel to them.
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