Let me say at the start that I am sure all three lines are excellent and that I am not looking for a flame war. These three lines have been recommended to me and have trips that look pretty similar, though not identical. I am looking at a round trip to/from either Vancouver or Seattle.
I have already seen some excellent info from Mike from Merced - thanks! Anyone who has experience or maybe can offer comparison of taking trips to Alaska on these three lines, let me know. In what ways might the experience be different? One thing I notice is size of ship. Another is that some trips seem to go open ocean to/from their start and end point (Princess from Seattle) and others go Inside Passage all the way to/from Vancouver. Does that matter a lot?
Cruising from VAncouver over Seattle is truly a totally different cruise expierence. Have done it from both on Princess and Celebrity and much prefer going from Vancouver and cruising the inside. I know when going from Seattle said inside, but it seemed anything but. I did visit Hubbard Glacier and it was amazing. The last cruise, on Princess went through Tracy Arm, which was enjoyable, but nothing like Hubbard Glacier..
We've sailed to Alaska on HAL, Celebrity, and NCL. We were happy with all 3. I'm sure we'd be happy with Princess too. We loved Hubbard Glacier. We loved Glacier bay more. Celebrity doesn't go to Glacier bay. HAL and Princess do although not every ship.
As Donna said, sailing round trip from Vancouver is much more "inside" than the trip from Seattle. Also you hit open sea on the route to Hubbard Glacier. So if you have sea sickness concerns you'd be better sailing from Vancouver and including Glacier bay. Of course, you're on the ocean and never can predict the weather.
The difference you are speaking of in "Inside Passage" cruises refers to Vancouver Island. Ships departing Vancouver are inside the island and cruise a narrow passage to pass it, then continue into the Inside Passage.
Ships from Seattle normally take the route outside Vancouver Island. They are indeed exposed to rougher seas and less scenery. Usually they compensate for that by stopping at Victoria, a really nice port. Often they also go to Sitka which is a port we love.
Here it is in a nutshell:
The two times we have encountered really rough seas in Alaska have been outside Vancouver Island, and enroute to Anchorage across the Gulf of Alaska. So if seasickness is your major concern, the "classic" Vancouver roundtrip would be the best choice.