I say Minecraft. Unlimited hours of play, no end to the game, even after The End.
Even though Minecraft is released, it has and still will receive updates in the future, constantly improving on the game. As for Skyward Sword, you'll play it, beat it, do the side quests, possibly do Hero Mode, and not play another play-through for at least another year. In the meantime, you'll probably still be playing Minecraft, so it's a better investment.