Do a back to back and then give us a report!
Seriously, you will get all answers here.
Personally, Vancouver is the port to sail from. You will see more of the Inside Passage from Vancouver than from Seattle.
Also, if you want to see something wonderful, take an extra day or two, ride the ferry to Victoria and visit Butchart Gardens.
Carnival Spirit 2003 (Caribbean)
Carnival Fascination 2004 (Caribbean)
HAL Noordam 2004 (Norway)
Celebrity Horizon 2005 (Caribbean)
Sun Princess 2006 (Caribbean)
Diamond Princess 2007 (Alaska)
Carnival Splendor 2008 (Mediterranean)