"You Say Run" from My Hero Academia is now my favorite anime OST without vocals.

This, coupled with "Eren's Berserk" from Attack On Titan are the best.

https://youtu.be/LmPH8BTwPKU

And of course, don't forget Ash-Greninja from Pokemon XYZ! 

https://youtu.be/SW7QU72Eo2s

Three reasons to prove the title. And I'm pretty sure these are the best ones I can find. ^D

~Hero