Tough decision. Bragging rights (not THAT big of a deal, but...) would be the Dalton. Overall beauty for me was Dempster. Dempster seemed more of a challenge. Either one will kick your hiney if they are significantly wet.
Dempster had so many changing views....almost like a different part of the world with each turn. Yes, the ferry crossings are each a gem. Inuvik is certainly a better place to overnight. Ain't nothing to see on the "Slope" really. Even though you are at the northern-most point, you really aren't as you can't go poke your toes in the Arctic anymore.
Either way it's an adventure you won't forget. Seems like I did both in a huge hurry. If I had to do it all again, I'd likely go slower and take a better camera.....but then I wouldn't get to haul ass and that has a joy all it's own.
Saw LOTS more animals on the Dempster.