use betton quest if u can write...
or use the quest plugin if u want to write ingame :P

Well... First the obvious: if you try and get a grip on the way command blocks (and functions) work, optionally with advantages, then you might not even need a plugin to do this. Commands can make mobs talk, advancements can be set to require certain tasks to bo completed before you'll receive a reward, stuff like that. The best part (but this isn't a thing just yet) is that you'll eventually be able to combine all of those (functions, advancements) into datapacks which makes them easier to use. This is going to become a thing in 1.13.

But to actually answer your question: I quite like the Quests plugin, it's still being maintained and runs on current Spigot versions. It even works pretty well together with Citizens, the plugin is pretty much outdated (as you can see it's for 1.10) but still runs on 1.12.2. The best part is that you can use these two plugins together (for example: place a NPC somewhere and then make it start a quest).