It jut depends upon my mood. For some good old head-banging metal, it's Nightwish or Rammstein. For bombastic orchestral music, it's Two Steps From Hell. For Folk-Rock, it's the Lumineers or Of Monsters and Men. For Pop-Rock, it's Lady Gaga, Shakira or, Florence and he Machine. For R&B/Jazz, its Emily Sande, Macy Gray and Aretha Franklin. For Classical, its Mozart. For Opera, its Sarah Brightman. For Bluegrass/Country Blues, its Mean Mary James, The Dead South and Reverend Peyton's Big Damn Band.
This isn't an instrumental...but pink floyd has these black ladies singing background vocals who are just fantastic.
On their live album "delicate sound of thunder" the ladies sing a part alone by themselves (I thunk the song is dogs of war)...it's just phenomenal! I need to pull out the old vinyl & listen to that again.
Technically, most of what has been listed can't be described as rock instrumentals (Bach?),
They are, however, examples of how a person would be unfair to himself to limit his listening to only one style.