Annihilation is the best spec for pre 50 warzones until 40, then it evens out quite a bit more. Rage has the highest damage potential when you are against a melee heavy team. Against a ranged team you will be hitting a single target with smash most of the time, which isn't exactly the best use of the spec. This is why i stopped playing it. Plus smash is still bugged.
Ive tried all three since i hit 40 and i can say they are all very effective. None more so than the other. Ive done 400k damage games with all 3 specs.
Its a different story at 50, but it is so imbalanced and broken that i haven't bothered playing in that bracket since Jan.
I would just try all 3 specs once you hit 40 for a while and see which one you enjoy the most. The damage difference is minimal if you are a decent player.