chess
best game played by grandmaster
Depends on the style you like, My oppinion is that chess from the old days hasnt been up to date with the current theory. I would reccommend watching certain M. Carlsen games where he shows his great understanding of the pieces and beautifull positional play. Exchange sacrifices.
Example https://www.youtube.com/watch?v=8adZ4jEw44I

I always liked kasparovs immortal

Here are two of my candidates for best game of 2015:
The first is Wei Yi's brilliancy against Bruzon:
His Chess Kings game against Bu Xiangzhi (~56 move win as white) was also a brilliancy.
According to you which is the best game played by grandmasters?