It really depends on what you want to do in the evening, and when you want to do it. We like the late seating because it gives us leisure time in the early evening - which means we don't have to rush around at the end of a port day to get ready for dinner, or can linger on the open decks during the sea days while the early seating people all leave to shower and dress.
But, early seating is good for those who wish to get dinner out of the way and can then have the whole evening open to hit all the clubs or the casino. Those with young kids usually opt for early seating, but we found that our son actually is a late eater and so we have been late seating people for the past ten years. We prefer it that way.