Forge is a powerfull modding toolchain for Minecraft nad more games. It allows mod developers to use their mods in a powerfull modding engine, so they can test the mods capabilty. It is also useful it you want to mod your server because forge is so powerfull you can add alot of mods
However forge is not the best for smaller servers because of its huge dependencies in your Minecraft server. It requires around 6GB of RAM at least for a smoother game.
If this is not your style however, and you want to play with plugins or lightweight mods, then you can use Fabric for lightweigth modding, if you want to use plugins then Paper is a stable option. If you don't want to use mods or plugins then Vanilla is the best option.