When I think back to the five times I've seen Becoming 2 and the Gift, Becoming 2 made my eyes water 3 of the 5 times. The Gift scores a perfect 5.
Grave doesn't score as well on the eyes-watering meter, but it scores well elsewhere. I score it a perfect 5 on the thinking deep thoughts meter. Every time I watch that episode, I find my mind wondering back to reality about a 1/2 hour later after thinking deep thoughts.
This happens to be my personal priority, so I'm going to choose Grave.
Also with Grave, I can't think of another episode that made me want to see what was going to happen next as badly as I did after watching Grave.