You can use either a zombie or a pillager to scare the villagers in a iron farm. As far as i know they spawn the same ammount of iron golems but pillagers don't burn in the sun. Also there is a complex mechanic behind the scare times and when he should and shouldn't be scaring but im not going to explain that. It is almost 100% efficient and 10x easier to just do a peice of souls sand with water on top.