I would recommend Princess with HAL a close second for a cruise to Alaska. My opinion is that Glacier Bay National Park is the highlight on any Alaskan cruise. Both Princess and HAL are allowed to sail into Glacier Bay and many of their cruises offer a second day of glacier cruising in College Fjord.
One thing to keep in mind that an Alaskan cruise, on any cruise line, is not like a cruise to the Caribbean. The average age will be slightly older. While there is night life it usually ends fairly early as most passengers rest up for the next days activities in port.