I usually grab something in the Concierge Lounge for breakfast and then lunch and dinner in the Windjammer. I used to do early seating and all meals in the dining room, no longer pack for that. I'm an "overhead bin suitcase person" since the day my suitcase was diverted for 6 days on a transatlantic and I had no clothes until Nice...never again.
Dinner at main dining room, or when traveling in a suite, the restaurant assigned for suite guests. I prefer to ear early. A visit to an specialty restaurant is a must, usually 1-3 nights. Breakfast at buffet, also lunch or some burger or hotdog at poolside.
Early - especially if we have an early AM excursion the next day. We usually cruise with Regent so Speciality Restaurants don't charge extra. We usually go to all available if not a couple twice when on board. NEVER do we do the Buffet!
Funny thing, we prefer any of the alternative dining areas usually. After all we are on vacation and travel with NO time pieces while on board. It's not that we don't like the main dining rooms, we just like total spontaneity, it the there is a 5 minute or more wait, we just look elsewhere. Or we make reservations to our favorite Steakhouse on board (have to use a clock then, ugh)