I have only ever had late seating.. but I can try to give you some of the pros and cons to both.
Pros to late seating:
1)More time in afternoon to do stuff. You don't have to rush back to your room to be ready for an early dinner.
2)Dinner is less rushed, since they don't have to get everyone out at a certain time.
Cons to late seating:
1)It might be later then you usually eat, especially with young children, who might fall asleep at the table, or be cranky because dinner will last until 9:30 sometimes.
2)To some being so full makes them tired, and want to go to sleep. Uusually what I did after dinner was take a walk on deck 4, or on deck 10 and let my food digest. I was usually feeling less full by the time the evening adult activities started. Or a lot of times I would catch the late movie or go relax in the pool, which is usually deserted by then. Quiet Cove is open until 12am!!
Pros to early seating:
1)Its around the normal time you eat, and you have plenty of time for your food to digest before evening activities begin
2)Might be better for younger children, who are more awake at that time, and will be able to enjoy meal more.
cons to early seating:
1)you'll have to get ready earlier, might make the afternoon feel rushed
2)I have heard the meal might be rushed, because they have to be done in time to clear and set up for the 2nd seating
Hopefully someone will be able to give you a better take on 1st seating. I have always been very happy with 2nd seating. And your daughter is older, so being up later won't be a problem!