The attraction for me with Carnival is that it is a pretty darned consistant product. I generally know the product I am buying, what they offer and the fact that not too much changes. I have grown to appreciate that. They have a darned good kids program too and that has also been very consistant over the years. I have no major complaints with Carnival other than they were slipping for a while on maintenance of their older ship, but several have gone into drydock for renovations since then. I trust that has been cared for.
NCL is all about variety. I like the number of eating venues I can choose from and have been known to get spoiled rotten by some of the staff. Many of NCL's staff have stuck with me and we have sailed with a few of the same folks a couple of times. Some passengers knock the freestyle aspect by saying they will miss having the same table/waitstaff every night. Because we like a lot of the speciality dining options, by the end of our last 14 day cruise, most of the staff at the restaurants knew us by name, I have to say from that aspect it was far from impersonal. as a matter of fact one MaitreD knew we had some issues one evening and provided us with priority seating because of a problem that another department had caused which would have likely resulted in us having a very late dinner or missing it completely.
NCL can really spoil you if you are booked in some of the nicer staterooms (or they have assigned you VIP status
) and in those cases you really do feel spoiled... I have at times found their kids program to offer much less than Carnival, on some ships I would gauge it as equal, even though NCL's facilities are nicer. But it is all about the staff. Sometimes you win, sometimes you don't with NCL's kids program it just depends.
But you really can't lose. You will have a great time on either line. I would recommend any of the newer NCL ships if you do choose NCL. With Carnival I would just ensure the ship is newer or has drydocked in the past year.