Overall I would probably choose NCL over Carnival. However I would not sail Epic again unless it was a fantastic itinerary or a Villa suite. I did not like the cabin on Epic nor the crowded feeling I got from the ship. I did enjoy the multiple dining venues and the variety of entertainment.
I like NCL because of the Freestyle concept that includes multiple dining venues plus I don't like being chased out my cabin at 8:00 a.m. as I was on my last Carnival cruise.
Don't get me wrong I like Carnival. I'm sailing the Liberty next March. But overall I prefere, non-Epic, NCL.