Whitewater is probably my favorite overall soundtrack. I don't think there have been any other games that implement their music quite like WH2O. I love how advancing up the river makes the main theme progressively change and get more exciting, and then there are lots of little touches like how, when you start multiball, the balls eject in time to the music. It's Chris Granner's best work IMO.
As for my most favorite single track in pinball, that's probably either Lost in the Zone or Swords of Fury with two balls locked.