I agree with those who would recommend avoiding RCCL and NCL.
We like Princess and Holland America. We put Alaska ports and itinerary first and not the ship. We love Alaska more than the Caribbean. I also never thought I would say that. We would love to do Un-Cruise in the future.
I would recommend doing a 1 way cruise and not round trip Seattle trips. You will get better times in ports, longer port days and more glacier days.