I am in a somewhat similar situation. I want to do Alaska next June and I have narrowed it down to NCL Encore and Discovery Princess. I they have the same itineraries. My husband and I are in our late 40’s. But we are traveling with two people in their 20’s. I think they would enjoy NCL more since there are more things to do on board. Princess tends to have an older crowd so they will probably be bored.
However, the ward cove situation with NCL really annoys me. It’s about 15-20 minutes by shuttle each way so less time in Ketchikan and that doesn’t include how long you will have to wait to get on the shuttle. Princess is right there in town which will be much easier for your father.
Also, in Juneau, NCL docks at the last pier which I think is a 15 minute walk. Im not sure if there is a shuttle. Princess again is right in town.
I don’t know about the dock situation in Skagway.
So I think in my case the ship experience would be better on NCL but the port experience would be better on Princess. If I were going with my parents who are in their 70’s (my dad has bad knees so he can’t walk too far), I would pick Princess since the ports are more convenient.
As for me, maybe I’ll let the younger ones decide.