It's deffo r/Flairwars and r/Num for me, despite not having been in the latter in the time I was on that site.
Both have their own unique inside jokes, battling systems, lore, fanworks, and most of all, a slow yet steadily thriving community that's accepting of everyone. I often wonder how my first aforementioned community would thrive in this vast federated space, especially with all the new possibilities out here... Maybe new lore expansions, and a reinvigoration on the way?