Shannon, I haven't been on the Nordic Empress but have been on the Inspiration twice. The Inspiration is a newer ship and has a gross tonnage of 73,000 tons, as compared to 48000 tons for the Nordic.
From what I have heard, the cabins on the Nordic are small and the soundproofing supposedly isn't good.
I personally would have to pick the Inspiration because as I said I have sailed it twice and know what it is, but that's just me. Have you sailed on any other Carnival "Fantasy" class ships, such as Sensation, Fascination, Imagination, etc, if so, the Inspiration is exactly the same except for the decor.
Good luck on whichever you end up on.