I don't know if it's my favorite, but "Earendil was a Mariner" / "Errantry" is simply astounding.
Proabably the most stirring for me is the pairing of Eomer's "Out of doubt, out of dark to the day's rising..." and the mourning song closing the same chapter.
Long now they sleep
under grass in Gondor by the Great River.
Grey now as tears, gleaming silver,
red then it rolled, roaring water:
foam dyed with blood flamed at sunset;
as beacons' mountains burned at evening;
red fell the dew in Rammas Echor.