It depends on the ship's plot. Depending on the plot, it is about 50/50. On our HI cruise, we had a starboard cabin and it was good for most of the voyage.
However, at least on our cruise, if you wanted to see the volcano spitting lava at night, the port side was better.
SS Norway (12 times) '85 - '97; Radiance OS 06/01; Island Princess 11/04, Grand Princess 11/04/05, Golden Princess 7/21/06, Golden Princess 2/24/07, Explorer of the Seas 12/23/07, Island Princess 11/15/08