It really doesn't matter, since you are in the inland passage on the Alaskan cruise, and you can see land from both sides of the ship. What is on the starboard side of the ship on the way up will be on the port side of the ship on the way back and vice versa.
Agree with the PP that it really doesn't matter since it's a round trip. About the only difference you might encounter is when the ship is docked in a port. Even then it's really not a big issue as the views are good all around and you can easily walk over to the other side of the ship just to see for your self.
Starboard if you're on an upper deck and forward. The port forward side is where the designated smoking area is, and on Glacier day people camp out there and smoke and ash drifts down to the balconies directly below.
GET UP TO A $1000 SHIPBOARD CREDIT AND AN EXCLUSIVE GIFT!
If you make your Disney Cruise Line reservation with Dreams Unlimited Travel you’ll receive these incredible shipboard credits to spend on your cruise!