2011 by faaaaaar. The amount of AAA games released that year was absolutely mind boggling. All platforms had something.
PC-Witcher 2, Star Wars MMO
PS3- Uncharted 3, Killzone 3, Little Big Planet 2, Resistance 3, Infamous 2
Xbox 360- Gears of War 3
Wii- Zelda Skyward Sword
3DS- Super Mario 3D Land
Not to mention the never-ending amount of third party games like Skyrim, Dark Souls, Modern Warfare 3, Battlefield 3, Arkham City, Dead Space 2, Portal 2, Deus Ex Human Revolution, Crisis 2, L.A. Noire, Assassin's Creed Revelations, Saints Row 3, Rayman Origins, and Mortal Kombat 9.
I would definitely say 2017 comes close but in terms of pure AAA games 2011 hands down. 2011 was absolute madness