I will say this - itinerary is the main thing. I would look for a cruise that goes to Glacier Bay (not Tracy Arm). The last time I was scheduled to go to Tracy Arm we were blocked from reaching the glacier.
Having said that, I suggest taking a smaller ship - Holland America, or an older Princess ship, because in Alaska the main things are
1) ability to navigate to the glaciers
2) ability to get on the right tours
So, with a small ship I think you will see more of Alaska than on a large ship. I like Holland America personally. I would rather take Princess in the Caribbean or Europe.