There really is no preferable side. We've cruised the Eastern twice, and from reading other responses, it's clear that the ship will dock from either side in any port. We sailed port, then starboard, and both times at Castaway Cay, the port side faced the main part of the island, and the starboard side faced the dock. That's the opposite of what someone else posted. So, I don't think there's any way to know how you will be oriented.
I think you should worry more about forward, midship, or aft and if there's anything you might be above or below.