Biggest cruise ship in the us?

Original answer from 2009: Currently there are three. Royal Caribbean's Freedom class made up of Freedom, Liberty and Independence of the Seas.

As of April 2011, the two biggest ships are the Royal Caribbean Oasis of the Seas and the Allure of the Seas. They are virtually identical sister ships, both listed at 225,282 Gross Registered Tons. The Allure is actually just a couple of inches longer than the Oasis.