Horde is pretty popping too. If you check out the link here, for example, our guild is doing something pretty much every night ranging from casual social stuff to adventure/combat to server events.
And that’s only a fraction of it. We’re not the only ones doing stuff.
It’s not easy to gauge by forum activity, though. Most of the stuff that happens gets spread by word of mouth in game, through guilds, or various social media subgroups. If you really want a feel, I suggest making a trial character and doing some exploring with friends. Ask around in game.