I personally, prefer the smaller RCI ships. Less crowds, and just a nicer atmosphere IMO. As the other posters have noted, the ports of call are better on the Serenade as well. I'd prefer the SOS, even though the ice show is the "star attraction" aboard the ships that have the ice rink. SOS entertainment will be excellent as well.
Marine, Pilot, Singer, Tuba Player, Carnival "Diamond"!