Agreed... The Deyja/Bracada theme is a great track. I'm also fond of many of the choral/piano pieces.Celeste is certainly tranquil, but I find the Pit's melody (particularly the symphonic crescendo) to be more moving. My opinions of the music, of course, stand independent of my preferences for Light or Dark.
RPCtH's point is well-taken... the Titan's Stronghold/Tunnel to Eeofel track is another memorable one. It certainly injects a feeling of levity into the otherwise unpleasant prospect of being squashed to bits.
My personal favorite, though, is probably the Harmondale theme. I think it's a severely underappreciated piece of music.