I cast my vote for the late Tommy Makem's rendition of "Johnny I Hardly Knew Ya'" as well as "Mrs. McGrath". Of course Eric Bogle's epic. To me the best songs are the least breast-beating and the most folk-concise. I'll put in for Derroll Adam's "Portland Town" since I knew Derroll about the time he wrote it and we had long talks about the futility of war.
Tommy Sand's "There Were Roses" and "The Music of Healing" gets my vote too.

Any good anti-war song is the greatest song ever in my book.

Frank Hamilton