First to vote! :p
BG: Isle of Conquest
That battleground has GREAT potential and all the events are fun, each point is unique to capture and the gunship assault is really immersive. Sadly it's ruined by the "RUSH BOSS AJAJAJAJAJ" people.
Arena: Ruins of Lordaeron
Why? It's really hated for most people, but if you get tired of the enemy team LoSing all your casts you can simply stay back and lure them, if not, they're risking to go to dampening and most likely lose. yes, this is biased because I'm a destro lock and hate LoS