Well for me it's Black Rock Shooter, but I have still yet to see all the anime they have released this year. So far I have only watched about half the anime that came out this year (god damn you work!).
Why hasn't anyone mentioned Kuroko no Basuke its one of the best animes this year!! Another was also an excellent mystery and horror series as well. I personally also like Chuunibyou Demo Koi ga Shitai, K, Tonari no Kaibutsu kun, Magi and pretty much most of this seasons anime :)