Millenium (one of the top PvP guilds in Europe) and Nihilum (the top PvE guild in the world, though they've recently started participating in the arena). The results? Millenium's extensive PvP let them sweep the match, defeating Nihlium 5-0. For more pictures an info on the match, check the official ESWC page on WoW's European site.
[via Curse Gaming]
Update: As pointed out in our comments, this is a repost. For Elizabeth Wachowski's take on the topic, check her post on the subject.