Because you are cruising with kids I would recommend giving Princess a shot. I know you didn't have that one on your list, but Princess and HAL have been doing Alaska the longest and know how to do it right. I just don't think HAL is the best fit for families, even during the summer. After the 2 listed I would suggest NCL, followed by Celebrity and RCI. Carnival isn't one of the lines that does that much in Alaska. It is important when picking a line you give consideration to which have the most experience with certain itineraries.
Just my opinion..
ncl, carnival, HAL, Costa, RCI, commodore,chamdres,celebrity,Princess