We've booked on Carnival for 28 Aug cruisetour, through cruisesonly.com. Main reasons we choose Carnival is I wanted to go to Sitka, for the Russian history. Gave up Glacier Bay for that, but I've seen many glaciers before. They also offer the 2 nights in Denali. Ended up with an aft balcony cabin, since most in our price range were gone (port side, anyway). We wanted a balcony, and not just a window, and Carnival's balconies are often around the same price as Princess or RCL's Ocean Views - at least in my research. If you get an ocean view or balcony, get port side for southbound trip and starboard for north bound.
Additionally, we liked the interior pictures of the ship, and both of us enjoyed Carnival cruises before. We found that we hated freestyle cruising on Norwegian, since on our ship, everyone wanted to eat at the same time, resulting in 40 min waits for tables. Also thought the service suffered since they put all tips into a central fund, rather than having passengers tip each person individually. Practically never saw our cabin steward on Norwegian. Can't coment on Holland or Princess - haven't done those yet.
Having grown up in Alaska (6 years), I personally wouldn't miss McKinley (sorry, Denali now). But take binoculars and long distance lens for your camera. You may or may not see the mountain, since it makes it's own weather and seems to like hiding behind clouds most days.
