I definitely agree with Mike about Holland America or Princess for Alaska.
Holland America has been doing Alaska longer than any other cruise line. They have the most ships there and the biggest presence. Their cruisetours are wonderful.
Princess has the second biggest presence in Alaska and has some very nice ships there.
I'm 64 and for us, it's tough to beat Celebrity and Holland America because they offer some a nice relaxing experience with great food and wonderful ships. So I'm showing my prejudice here when I say it's really tough to beat Holland America when looking at Alaska.
As Mike pointed out, there are many options to consider and one of them would have to be whether you want to do a roundtrip or one-way cruise. One-way cruises will give you the opportunity to spend some time in Alaska if you would like to go up and see Anchorage, Denaili, and/or Fairbanks, especially by train.
Talk to your agent, preferably one who's been there, so they can help you with the many different opportunities available to you.