Best plugins Minecraft?

There are a few core plugins, without them some server wouldn't exist. These are Essentials (or EssentialsX), Worldedit (maybe VoxelSniper), Vault, ProtocolLib (this is just a library, but also it can be a really powerful developertool), MultiverseCore (the addons are also great, like MultiversePortals, MultiverseNetherPortals, etc...) and Skript.
For survival servers I would recommend Craftbook and MyPet, both are insanely good plugins.