I went with Xenoblade Chronicles since it's my favorite game of all time, and improved textures, lighting, and a more consistent frame rate would be one of those rare times when you CAN improve on what I already consider to basically be a perfect game.
I was REALLY tempted to say Twilight Princess or Skyward Sword as Zelda is my fav franchise, but I would rather they do a "double-pack" and give TP AND SS the HD treatment and bundle them together for the $50-$60 price of one game.
Upcoming Games To Get
Definite: Kirby Star Allies (Switch), Mario Tennis Aces (Switch), Fire Emblem (Switch), Yoshi (Switch), Pokemon (Switch), Kingdom Hearts 3 (PS4), Monster Hunter World (PS4)
Considering: Fe (Switch), Donkey Kong Country Tropical Freeze (Switch), The World Ends With You (Switch), Ys VIII (Switch), Street Fighter V: Arcade Edition (PS4), Kingdom Hearts 2.8 Remix (PS4), The Last Guardian (PS4), Shadow of the Colossus HD (PS4), Anthem (PS4), Shenmue 3 (PS4), WiLD (PS4)