If there are 2 of you travelling, I recommend a balcony room. it gives you much more of a sense of openess than an inside cabin does, and you can get fresh, non-airconditioned air anytime you like.
I usually book myself a room with a balcony, but i did my last cruise in an inside room and wasn't as happy there without a view/fresh air. It is also nice to know what it is like outside, before you leave your cabin LOL.
Since the rooms on the NCL ships are smaller than the HAL ships, get as large a room as you can afford comfortably.
cheers
jan,eh!