As always, it depends on what seats are open. I'd generally opt for the 777 since it's a bit of a novelty when flying domestic. However, it has the same angle/flat seats as the 767, and the 777 has 2 potential drawbacks- 1, if it's already fairly full, you want to be able to avoid the middle seat in the center section of the 2-3-2 configuration, and there's more people in the cabin (I believe) or at least more in premium seats generally, so depending on how crowded it is, the service may be stretched.