I'm not sure that there is a best...there are so many and a lot come close
but there are three I'd like to mention, and this can also be tied to the 'forgotten songwriter' thread

"Long Black Veil" sung by Lefty Frizzel written by Danny Dill/Marijohn Wilken

"I Never go Around Mirrors" covered by Lefty Frizzel, Keith Whitly, Merle Haggard, Gene Watson, Mark Chesnut.. written by Whitey Shafer

"Farewell Party" sung by Gene Watson, written by Lawton Williams