For me I look at the itinerary. If the cruise is port heavy- Then I really don't need the ship to entertain me. I know we will be exhausted and want dinner, a drink and bed!
I did Alaska 20 years ago (wow that hurts saying it out loud lol) and it was a trip of a lifetime. For alaska you must have a balcony! We sat on ours each night and watched the shore, the sealife and waves each night! Many times not realizing it was past midnight (daylight all the time!) with 8am tours. The cruise provided blankets for sitting outside!
You have to realize that you will not be in the pool!
We booked all our own excursions. Went on a whale sightseeing trip with only 4 people. Again a trip of a lifetime!
So to answer your question.. look at the stops and book based on that!