I think we'll eat first, since the earlier dining times tend to be easier to get, and we want to avoid the dining crowds as much as possible. Service seems to be quicker the earlier you dine. I like to get the first ADR at restaurant opening. Besides, the earlier I eat, the less hungry I get, the less likely I am to overeat, and the cheaper it is (we're not using the Dining Plan...it's too much of a temptation to overeat, for me.).
Besides, I'm hoping to do other things in the evening, and the earlier we eat, the earlier we can see CP (planning on 6:45 p.m.), and the more likely we'll have a full evening to set up other things to do (maybe the Illuminations cruise!).