With Alaska, go with price and itinerary over cruise line, and if you want to use a pool make sure the ship you choose has a covered pool (one with a magrodome roof). The ship is mostly your hotel and evening dinner in Alaska and the cruise should be all about the scenery and land excursions. Excursions in Alaska are not cheap and you can easily pay more for the tours than you did for the cruise itself.
All the above said, the cruise line with the most experience in Alaska is Princess. Ideally, the best way to do Alaska is on a cruisetour where you have a few days inland, taking cruise line trains and buses to various places. I'm going next July on Celebrity, from Anchorage to Vancouver, with 4 days of touring before we board the ship. It is all included in the cruise price, including buses, train, hotels. But, in a balcony cabin it is $6500 for two, and as I said, once the cruise starts, I'll have to pay for the tours I take in the ports.
For a first timer, you might want to look at a round trip from Seattle to the Inside Passage. It's less complicated. Don't forget that even though it is a cruise to Alaska, you can still have a need for passports to travel, depending on the itinerary you choose. There are also some tours (a couple in Skagway come to mind) that go into Canada and require a passport.