I had a lot of suggestions until you wrote against Sylvanas! You will find a lot of high quality guilds on the server that are Sylvanas loyal, and can find them in the Stygian Legion thread.
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A guild that is against Sylvanas and in a rebellion is Frozen Paw Clan. I have never been in the guild but interactions in Orgrimmar so far have been fun. They are currently in a clash against the Stygian Legion for going against Sylvanas, and they are pretty active, so if its open rebellion you are looking for with other races of the horde, you might want to seek them out! [H-RP]The Frozen Paw Clan - A Light in the Darkness 🔥
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If you look for troll-based guild I cannot recommend Shadow of the Empires enough. One of the older trollguilds on the server but active daily, friendly people and very friendly for beginners, they really spend a lot of time on newcomers and new characters and build plotplines around the trolls in their roster, so they would definitely able to help you with your troll. They do plenty of events but since they’re non-horde they are mostly situated in Stranglethorn, so adventures will mostly be jungle based.
[Troll RP] Shadow of the Empires - 8 years of troll RP! - back in Zul'Gurub -
If you want Zandalari RP, you can check out The First Empire and Reach of the Empire, both are big Zandalari themed guilds loyal to Talanji as far as I know, and while they do not actively oppose Sylvanas they don’t side with her. Both are new and have a lot of trolls! Since they’ve just started I can’t tell you much about their events, but they will travel the world a lot from what I understood. The First Empire [Zandalari RP]
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There is also Hand of Zanchul, non-horde troll extremists and slavers, taking Horde-races in as slaves. Also a new guild with a lot of people around. Like the other Zandalari guilds they have just started but will travel a lot. [H-RP] Hand of Zanchul (Zandalari/Troll/Slave Guild)
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Zul Guede and Gravesworn are both troll guild about the Loa of Death, Bwonsamdi. Both seem fun but I don’t know too much about them or if they suit your character!
I don’t know any of the smaller adventurer guilds so hopefully someone can help you with that!