They are almost identical as far as just cruising in the Passage. You will have land far off on both sides. For viewing wildlife, its' hard. you are going to need a excellent pair of binoculars to start with, If you think about, wildlife is wild they don't stay in one place! If scenery and wildlife are a priority, then side viewing isn't the best option, you need full front and the ability to track from ahead
If you are sailing one way northbound, the cabins on the Starboard side are more popular, while Port cabins are more popular on southbound sailings.
There is generally land on both sides, so you will have scenery whichever side you choose.
Of course, most people go onto the top decks for the live commentary... but my choice is the Promenade deck which is more sheltered and less crowded... also the glaciers look much more impressive from the lower viewpoint.
My choice, however, is the cheapest inside cabin, and the best cruise. Last time I got a 7 day northbound cruise in an inside cabin and a 5 day land tour by rail, for the price of an average outside - not balcony - cabin. When Princess upgraded me to an outside cabin it put a smile on my face... but I would rather be in the public rooms than on my balcony... except for in the Caribbean.
Another very popular viewing point is the lido buffet... panoramic windows and warmth too.
We had a rear balcony cabin and it was worth every penny. I am a photographer and I could take all the pictures I wanted. As the ship drifts around Glacier Bay or Hubbard Glacier (depends on the cruise line) you can see and hear everything. I also recommend a rear balcony cabin (dead centre if possible or on the edge) for Panama Canal cruises, North Cape, Hawaii and Polynesian Islands.
On our Alaskan cruises, we have never booked a cabin on the 'which side is best, criteria but have always looked at the position in relation to kitchens,theater,nightclub,casino,bars and other potential noisy areas. In our experience, Alaskan cruises can be quite energetic with hiking, kyaking etc and all that wonderful fresh air induces you to hit the sack earlier than on other cruises so a good night sleep without the jangling of casino slots, night owls in the bar or the banging of pans in the kitchen late at night is VIP.As you will be on deck for a good portion of the day sharing the experience with the other passengers it really does not matter which side you are on.Pack your camera and binoculars, a few fleecy layers and a light kagoul and have a wonderful trip.