Hs 293 as the most effective wartime guided weapon

What was the most effective drone or guided weapon of World War II?

Probably the German Hs 293, if radio-guided glide bombs are included, because it was produced and used operationally in substantial numbers.

Germany fielded guided weapons in meaningful numbers during the Second World War, which makes the Hs 293 the choice here. It was a radio-guided glide bomb rather than an autonomous drone, so the answer depends on treating guided weapons broadly. Its advantage is empirical: it was built and used often enough to demonstrate operational effectiveness. That qualification distinguishes remote guidance from later ideas of autonomous attack aircraft.