We've cruised to Alaska twice, both time on Princess. In 1994 (before we had kids), we did a 7-day cruise from Vancouver, BC. We stopped in Ketchican, Juneau and Skagway. We spent a day cruising Glacier Bay and another cruising the College Fjords (a passageway with a series of glaciers named after Ivy League Colleges). The cruise ended in Seward, Alaska and Princess bussed us about 4 hours to the Anchorage airport.
Just last June, we did a 10-day cruise with our boys (ages 12 and 9 at the time). This one was round-trip from San Francisco which was great since we only live an hour away. We did the same 3 ports and also stopped in Victoria, BC.
If you're interested in the Yukon & White Pass Railroad, make sure you choose a cruise that stops in Skagway. Some itineraries stop in Sitka instead since Skagway has limited space for ships in port. The train boards right in front of the cruise dock and takes you up the mountain pass and into Canada. The views are spectacular. On our first cruise, we walked into town after the train ride. This time, it was freezing cold and raining. My oldest is a train freak so he and his dad braved the cold to go to town and shop at the depot store. The youngest and I opted for the warmth of the afternoon snack buffet!
I would recommend Princess. We've been on 3 cruises with them and we are impressed with their service and their ships.