One thing to consider is how long you have in port and to make sure you are back to the ship in plenty of time before sail away. In general, private tours usually offer better value, either in smaller group, covering more territory, or longer time spent on tour. The downside is that Princess generally doesn't wait for late return of private tours, so if something unexpected happens to slow the tour down you could possibly miss the ship. This is a consideration for all cruises, but Alaska port times are usually generous enough to cover any setbacks on a private tour. Another consideration is if your travel insurance covers mishaps on private tours, and I don't know the answer.