For example, the original Layla and the acoustic cover by Clapton is one of the better combos. What is the best?
Layla was Clapton's song to begin with so if that was the question the intent of the thread is best covet of an artist's own previously recorded song
Re-recording your own song is not what a "cover" is. I don't like the acoustic Layla much because it omits the piano coda with the duel lead guitar between Clapton and Allman's bottleneck. Hard to do acoustically, perhaps, but half the song is gone.
Honestly, I like Pink Floyd's Welcome to the Machine and Shadows Fall rendition. Pink Floyd Shadows Fall
Sex Pistols - Anarchy In The UK - Megadeth Jefferson Airplane - White Rabbit - Grace Potter and the Nocturnals.