Man that is a question that only you can answer. Both are wonderful. Just depends on how you like your legs. On the deck looking at some of the most wonderful sights on earth, or having your legs in the air doing other things. Or just watching others having fun in the sack, or are you the one in the sack?
Having just returned from the Norwegian Sun, I don't know why everyone just assumes that they're a floating horror story.
Obviously, the Dawn cruise will be raucous and filled with hyjinks, camp and such. I love NCL's freestyle concept with no set dining hours and the the ship itself is gorgeous.
Crystal will be much more sedate and luxurious, and Alaska tends to be an early to bed-early to rise destination.
I'd say you've got to decide whether you want a week of non stop fun in the sun with an all gay crowd or 2 weeks in Alaska on a decidedly more conservative ship. Both options are great but they're about as diametrically opposed as you can get.