I've been to Alaska twice and the third trip is scheduled for July '23, so I am nowhere near an expert.
I would never do a trip out of Seattle because you miss too much of the inside passage.
I will never do a trip without Skagway because my husband loves the train trip.
I will only book a ship that has an aft balcony, the best views IMO.
We are doing our first one way next year, Southbound, which provides more port time and a port we've never been, Icy Strait Point. We were scheduled on another line but they cancelled Skagway so we switched to Celebrity, which we have cruised Alaska with before.
Just know, this won't be your only trip to Alaska, it's so beautiful, you will want to go back.