Don't necessarily believe everything you hear. Some people judge based on one persons opinion of one cruise that wasn't the greatest. We know all the horror stories out there about how horrible Carnival is yet they seem to have full ship all the time.
I sailed NCLA in Hawaii before they pulled the last 2 ships out of HI. I enjoyed my cruise a lot. Heard lots of complaints about how bad the service was and many people said regular NCL foreign ships aren't bad just the American flagged ships. People would say because American's are lazy and you get better service from foreigners. I take all those comments with a grain of salt. I enjoyed my cruise and would sail NCL again. However, I feel Carnival has more to offer as far as cabins. Their cabins, especially inside cabins, are much larger and more comfortable. I could have booked my next cruise on NCL for a little less $ but opted for Carnival because 4 people in a cabin on NCL would be wall to wall beds but Carnival has a much nicer setup with a lot more room to walk around.