Frank is right -- the Grandview Rail Transfer is an excellent choice. The train departs from right outside the cruise ship terminal.
The first two disembarkation groups are for the Grandview Rail Transfer to Anchorage. They call the first group at 6:00 and the second group at 6:15. Coming off the ship, you get into a queue in the terminal that leads to desk near the end of the teminal where the agent assigns coaches (designated by color) and seats within each coach (designated by number), then directs you to the train. Make sure that your whole party disembarks together if you want to be seated together on the train.
The rail transfer arrives at the train station in Anchorage around 11:30 AM. If you have an afternoon flight, you will have to go directly to the airport. Otherwise, you can check your luggage at Princess's hospitality room at the Egan Center, which is right in the center of town, get lunch at a real restaurant, and spend some time in the downtown area of Anchorage. Princess provides complementary transfers from the Egan Center to the airport every half hour until 6:30 PM, but you have to claim your luggage by 6:00 PM. Thus, you will have about five to six hours on your own if you have an evening flight.
I second all Frank's comments about the Grandview Rail Transfer. The scenery along the route is quite spectacular, too, so have your camera ready. I definitely will choose this option over the motorcoach transfer whenever I return to Alaska.
Have a great cruise!