I would have to say "Come By the Hills". It's an Irish traditional tune that I first heard played by Celtic Thunder on one of their CDs. I think because I live in the mountains that it really speaks to me.
But I also LOVE "River" too that several of you mentioned. Put the two together and you would need a whole box of tissues to handle the tears.
updated by @marsha-elliott: 07/31/18 02:56:46PM