I have cruised both directions several times. I prefer southbound for the daylight sailing of Inside Vancouver Island. Northbound is mostly sailed at night.
In making your choice, look also at port times. Longer is better most of the time.
IF you are sailing Glacier Bay and/or College Fjords AND ONLY want glacier viewing from your cabin, you need a port side cabin. But be aware the superior viewing is from outside decks, especially the front. Otherwise, it really doesn't matter what side, both at some point will have scenic sailing. Ships no longer sail "coastal" out of the Inside Passage, and many go open ocean.