I prefere to use these platforms/softwares (for minecraft) 17
Forum (16) 94%
Discord (10) 59%
Teamspeak (9) 53%
Twitter (2) 12%
Other (post comment about usefulness) (1) 6%
This is a difficult question. But i think that it will be the best way to create a hybrid. A Forum is the best way for a long term data storage. You can search for questions, create extended topics about your project/clan/servergroup and everyone can save this topic easy by the direct link.
Otherwise, discord is a platform to speak to someone very quickly and easily. If there are bigger clans, they need more channels than I would prefer Teamspeak. The authorization system and the complex channel structure are better in Teamspeak.
Maybe I would prefer the classic combination of forum + teamspeak. This gives you two separate functions for platforms. One to write about something and the other to talk about something. If you will use discord + forum there will be a big conflict. Because you dont know where you have to search better for your information and the community will choose one side and the other will fall asleep.
[Teamspeak+Forum] is better to scale than [Discord].