Although, as a quick protip, in space, the more inconspicuous the object, the more effective it will be. Trade ships carrying suicide tsar bomb payloads, a few hundree asteroids with thrusters on them built by self replicating drones hurled at a planet (as you only need one to hit to "win" as it were and it would be obscenely cheap to pull off.) Space wars would be more espionage and hitting the enemy so hard the first time they would be incapable of a retalitory strike. Otherwise, anything blatant and obvious like a space fleet of war ships is easily seen and countered long before it can reach you.