For me it would have to be the Dying Rebel. I was sat in the South Pole Inn, former home of, Tom Crean one of the greatest heroes Ireland produced, last year playing a few songs on my guitar when an old guy in his mid eighties, sang the song and the passion, sentiment and sadness that came across in his voice had me realising that although he can't have been present, it must have had a direct effect on him personally because tears were descending his cheeks as he sang. Maybe a family member had suffered in the rising but whatever it was his grief was personal apart from that he showed whilst singing the song
I'd never heard the song before but learned to play it and it has become a favourite song of mine.
I vote The Dying Rebel and thank an old man for introducing me to a beautiful song sang with meaning.