Maaaan I really love Gerudo Valley. It's so great.
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A lot to choose from. I think mine would have to be Requiem of Spirit, or Nocturne of Shadow. Or Ganondorf's theme. Or the Overworld/Hyrule Field theme. Gerudo Valley as well. Koume and Kotake theme is nice too. Boss battle themes. Deku Tree. Song of Storms. Epona's song.... God damn I can go on and on.