This thread is a good opportunity to list the exclusives I bought for each system:
The Legend of Zelda: Skyward Sword, Xenoblade Chronicles, Kirby's Epic Yarn, Disney Epic Mickey, Super Mario Galaxy 2, The Sky Crawlers: Innocent Aces, Endless Ocean: Blue World, Muramasa: The Demon Blade, The Legend of Zelda: Twilight Princess, Little King's Story, Endless Ocean, Super Smash Bros. Brawl, Metroid Prime 3: Corruption, Super Paper Mario, Mario Kart Wii, Zack & Wiki: Quest for Barbaros' Treasure, Super Mario Galaxy / Final Fantasy CC: King, Final Fantasy CC: Darklord, Art Style: light trax.
21 (18 / 3)
Afrika, Yakuza 3, Heavy Rain, Katamari Forever, Heavenly Sword, Uncharted 2: Among Thieves, Uncharted: Drake's Fortune, Valkyria Chronicles / Flower, Flow, Wipeout HD, Noby Noby Boy, Planet Minigolf, Cuboid, Hustle Kings, Malicious.
16 (8 / 8)
Fable II, Lost Odyssey, Halo Wars, Project Sylpheed, Kameo: Element of Power / Rez HD, Outpost Kaloki X, Arkedo Series 03 Pixel, A Kingdom for Keflings, ilomilo.
9 (4 / 5)
(I didn't count Wii Sports and Hexic HD as I most probably wouldn't have bought those two bundled games. Rereleaes I bought like Pikmin 1+2, ICO, Shadow of the Colossus didn't count either.)
So obviously Wii for me.
