This is a fun topic but very subjective, for sure. I cannot speak on ball of the year in 2016......we're not even half the way through!!
For me, just from observations, the BOY went like this:
2013: Primal Rage
2014: Melee Jab/Hyper Cell Skid
And 2015 was just off the charts.....too many great pieces out: Paradox/ Vandal/ Nirvana/Lock/Arson Hi-Flare/Gamebreaker 2!! I can't zero in on just one piece, since all these balls were making a lot of noise in 2015!!