Original Album -- Orchestra, mainly brass I hear, play in the background. The guitar solo is VERY loud and VERY powerful. The symbals echo in the second verse. They repeat the "There will be an answer, let it be," part at the end of the song, and they have the guitar play along at the end for two choruses.
Single -- They don't repeat the end, and instead of an orchestra, there's a different sort of sound. The guitar solo is more subdued.
Naked -- Paul's voice seems louder here. The guitar solo is quiter than Original album. They add some sort of instrument in the second verse during the, "For though they may be parted," You can hear guitar playing in the background in the last chorus, but I can't hear it that well, not like in the original version. No backing orchestra here.
