I would suggest that you do excursions that interest you - each port has different things they are known for but there are also excursions for every interest in any of them. Juneau is known for Mendenhall Glacier and whale watching - it also has some gold mining. Skagway is known for being a gold rush town - you can visit an old dredge, ride the White Pass RR or just walk around town and take in the history. In Victoria you can take a romantic horse drawn carrage ride, do a pub crawl, and if you have lots of time - visit the Buchart Gardens - they are great even at night. Havent been to Sitka so no reccomendations there. Good luck and enjoy your cruise.