Cruisers have devised a rule-of-thumb that if you are travelling southbound, you book portside and starboard of travelling north; and if you were cruising straight north or south, this would be good advice.
However, take a CLOSE look at a map of Alaska. To get from port to port you are cruising anything BUT north or south; and you often have land on both sides of the ship. And most ports you sail out the same way you sailed in, so the port/starboard theory just dosen't hold up.
Given your cabin choices, I would pick midship/starboard for its better location on the the ship.
By the way, hello and welcome to cruise-chat (how rude of me); is this your first cruise? What ship are you sailing on?
Any other questions, please ask. We all love to talk about cruising.