Freddie was the one who won, but gave it up to Missy to "protect iCarly." However, it was heavily implied that he did it for both Sam and Carly, since Sam was miserable when Missy kept trying to get rid of her as Carly's best friend and Carly was being tricked and used by Missy. This proved that Freddie really does care about Carly, Sam, and the trio's friendship.
Carly explained to Freddie that when she and Missy were younger, Missy used to get really seasick, but figures that she probably got over it since she was going on a cruise.
At the end of the episode, it's shown the trip isn't even close to being as glamorous as it's advertised to be--for example, unlike the advertisement photograph (which depicted the program as taking place on a luxury cruise ship or luxury ocean liner), it's revealed that the program actually takes on a cargo ship.
Also, in a bit of ironic karma, it's shown the Missy (despite having previously been very excited about "winning" the contest) still suffers from seasickness. Her only episode-appearance ends with her barfing over the side of the cargo ship and yelling, "Get me off this stupid boat!"