It's a tough choice between Mario Kart 8 and Dark Souls 2 for me. In the end, I'd say Mario Kart 8. Even though I haven't played Smash Bros. yet, I think that Mario Kart 8 was the best new game I've seen/played this year.
Mario Kart 8, Bayonetta 2 and Smash Bros for Wii U have the best chances of winning to me.
They'll have tough competition from Destiny, Titanfall, Dark Souls 2 and...COD?
You think it could happen? Mario 3D World almost won last year.