Neither.
Fully amortize the research and production of rail gun and directed energy weapons. Place on drones. Fly five hundred of them toward the enemy and each one sink or splash a target. Enemy gone, cost benefit through the roof.
Nope. Need both. The CBT is for power projection as well as protection of shipping lanes. The ARG is for establishing a beach head. Killing the enemy is only part of the puzzle. Land needs to be held and you can't do that with a rail gun.
Just how much energy will a drone be able to generate?
And what terminal effect would that have on a WARSHIP.
Better a conventional munition on a drone or a kamikazee drone.