To me, it depends on a couple of factors:
1) Where you are cruising
2) Where you are from
3) When you typically eat
For a Caribbean cruise, things are at earlier times for most (we're from the Central time zone), so immediately things are bumped an hour up. Second, when we go to the Atlantic time zone if on an eastern route, that's two hours, so a 5:30 p.m. dinner is like 3:30 p.m. to us.
Although, when we did Mexican Riviera we still did late seating because we are used to eating later, but I think we snacked more on that cruise than most.
In my opinion, late seating is better because the early seaters are busy eating and it gives you a couple of hours to do stuff with a half empty ship. Of course, on
DCL, that is mostly going to the show, but if you want to enjoy the deck and pool area, it will be far less congested. Not to say that it won't be after dinner either, but, for us, we use dinner as a wind down to our day.
We've got three kids 9, 6, 4 and they've been at various stages of life on our cruises. The kids 3-under, will usually sleep anywhere and we find two chairs to put together if they don't make it through dinner for them to sleep on.