Best Guess At Best
From Halopedia, the Halo wiki
Best Guess At Best is the seventeenth track in Halo Wars: Original Soundtrack.
The track is an ambient track featuring a mix of basses, percussion, and synthesizers with reverb as well as digital notes.
The soundtrack's bonus DVD includes an alternate version, titled Best Guess At Best (Shield Exterior Intro Version), featuring additional vocals, heavy percussive beats, and the main melody at a higher tempo.
The track plays randomly as a backing track during gameplay on any campaign or Skirmish levels in Halo Wars set on the surface of the Etran Harborage (though with exception of two campaign levels), including:
The alternate version only plays in the beginning of the levels listed above.