I did Princess for my latest one, and they were good. They're supposed to be the best cruise line for Alaska, from what I've read and heard.
You don't mention what you want to do, but I did a 7 day round trip from Seattle, Sunday to Sunday. If you are looking to avoid returning to Seattle altogether, then maybe look into doing one that returns into Vancouver. Bear in mind though if you do a cruise that returns into Vancouver leaving from Seattle, you MUST have a passport. If you do a closed loop cruise (returning to the same US port), then a driver's license and birth certificate should do if you don't have a passport.
2007 - Majesty of the Seas (Bahamas)
2009 - Enchantment of the Seas (Western Caribbean)
2010 - Freedom of the Seas (Western Caribbean)
2013 - Golden Princess (Alaska, roundtrip from Seattle)