A song murdered by someone.

I hate to say a bad word about these two, but:

Aretha covered the Beatle's Eleanor Rigby. I have it. Its pretty bad.

I also don't like Otis Redding's cover of I Can't Get No Satisfaction.

I do like Wilson Pickett's cover of Hey Jude with Dwayne Allman on guitar. Its a different song altogether which sometimes makes a cover okay.

Guns and Roses' version of McCartney's Live and Let Die.

I don't know if great songs can ever be murdered by a cover--they survive and the cover just makes one appreciate the artistry of the original artist even more.  I like almost all covers I hear of songs I like, but my least favorite form of covers, categorically speaking, involve opera singers doing operatic covers of popular songs.  I bought, and then only listened once, to Kiri Te Kanawa doing hits from "South Pacific;" it was funny, but not that funny that I wanted to hear it again.

The original version of "Unchained Melody" is so superior that the Righteous Brothers cover shouldn't be played? 

Only the Righteous Brother's version should be played. All hyperbole aside....I think it is the best and others fall short. But its music. People like what they like.