Do what you do at home. We eat around 8pm at home. It's always been late dining for us. I'm heading to Spain this Summer where they eat at 10pm. That will be an adjustment I'm usually in bed by then.
To each their own, but I'd like to give the other side of the coin. To me a cruise was so different than my normal routine that my normal dining habits didn't apply.
For instance, at home, I get up early, eat very little breakfast, and opt for early lunch and early dinner times.
But on a cruise, I get up a bit later, enjoy a nice breakfast (either in the MDR or buffet), have a nice sit down lunch, and so waiting later for dinner is much easier than it would normally be for me. Plus, we LOVED the treat of "Free" room service, so much different than any hotel you stay in. So we would often get wings or cheese plate or even a salad delivered to our room while we were dressing for dinner. Plus, the meal portion sized in the MDRs are not nearly as big as in many restaurants. Sure you can get more if you want it, that is fine. My point is, I often found myself eating a lot less for dinner in the MDRs than I would if I went out to a restaurant at home. Thus, many smaller meals, and abundant, no extra charge options, meant it didn't matter so much when dinner was.
To me, the choice of which dinner to have should be based on your Entertainment preferences. If you plan to be in bed by 10, do early dinner. If you want to stay up late, late dinner is great. Keep in mind too that there are a lot of activities that start at various times. This can be true for kids as well as adults, so check out some Navigators to see what works best for you. None of the big events happen during either dinner, but some of the smaller ones do, plus there is just a flow to events before or after dinner.