The PvP community is extremely active on both factions, and there are many PvP guilds doing daily activities with premades, open-world pvp and arenas.
Make a choice for yourself and don't listen to whoever thinks one faction is superior to the other.
Here's a list of currently active PvP guilds for both factions I'd recommend you checking out, some of them might be asking for requirements depending on your PvP experience.
Horde :
<Puff Puff Pass>, <Unmerciful>, <Immortal Outlaws>, <Unit X>
Alliance :
<Idc Gotta Farm>, <Carpe Noctem>, <POKEMONS>, <Old Division>, <Trauma>