This question is frequently asked, and it seems to get the most specific and ardent respondents. It seems folks will protect their decisions, be it early or late seating, with amazing zeal.
I personally would like to see if on my next cruise they would allow me to do both, early and late seating. Given a few minutes between seatings I'm sure I could hold up my end with courses consumed. I'd even be willing to tip my server's double.
Since early/main seating is first, let's examine the benefits I see in it. You get to eat earlier! That is enough of an attraction to me. To be honest Mrs. Kuki and I do prefer main seating dinner. I like to enjoy the ship's night life. I want to see the featured show in the showroom, check out the music in the various lounges onboard and still have time for the casino. And eating earlier seems to allow time to accomplish all of this.
On Caribbean sailing's especially, the ship seems to leave most of the ports of call by 5 or 6 PM, so the rush to get back to the ship isn't quite as bad as one might expect.
By reputation early seating attracts the older folks and families, and to a degree this is true. However, we see a lot these people taking late seating because they don't want to be perceived as fitting into the above categories. They want people to think they're still alive. But then, they're off to bed right after dinner.
We've also cruised with friends who insist they prefer late seating to be able to enjoy the sail away from ports of call, or sunsets at sea without having to rush to dress for dinner. In fact, they often spend those sail away's napping to try and build up energy to last to late seating dinner. Many cruise lines now hold at least some of the shows for late seating passengers prior to dinner, thereby negating some of the benefits of that extra time "late seating" advocates talk about.
One of the benefits that we early seating advocates used to find an effective argument was, if one ate early by the time the midnight buffet came around we could eat again. As though eating at midnight was a great reward. With many of the major cruise lines either doing away with the midnight buffet, or limiting the number of times they're held, the effectiveness of this argument is greatly diminished.
There is no question that late seating offers passengers more time to relax (read NAP), clean up, or enjoy the sunsets from the deck, or a late afternoon Jacuzzi, after returning from a busy day in a port of call.
Also late seating can be a more relaxed dining experience, as there's not another group coming into the dining room that the staff have to prepare for. In the past when we've had late seating there's been the occasion when we've had such great table mates that we didn't even leave the dining room much before midnight.
There is no one correct answer as to which dining time is best. You have to decide which factors are right for you. My personal opinion is that the itinerary that you're sailing should have a large part in your decision making. For example a Southern Caribbean, or Alaska itinerary which are very port intensive and active, probably lend themselves best to late seating. An itinerary with many sea days might lend itself best to early dining as the rush factor is basically eliminated and you do open up more time in the evening to enjoy the ship.
Now many of the cruise lines are offering alternate dining options for those that want a more casual dinner experience, or were too late returning from a port of call.
Gee, it's a tough decision! I think I'll stick to my idea of doing early AND late seating.