There are so many good ones... i have no favorites.
One OST I recently fell in love with is from a Japanese mobile game that is kind of obscure called:
Kidou Sentai Iron Saga; just released global not that long ago.
If you want straight-up Attack on Titan chills up your spinal column, listen to one of it's opening tracks:
Hiroyuki Sawano can do no wrong i swear.
But again, i have so much game music that i love, ranging from the Witcher series, to a bunch of underground Japanese game OST's, i love them all, i will not pick a favorite. xD