Should I learn Norwegian, Swedish, or Danish?

I would like to learn one of the 3. I know they are all similarly related, so if I know one,and if I want to learn one of the others, it won't be too hard. Which should I learn though? Which is more widely spoken, and which sounds the best? Also, which would be the most useful? I'm looking to move to a country in Scandinavia and knowing one of these will be useful.