Covering another artist's hits can be a tricky business. If you simply mimic their performance, you invite the wrath of those who have made a fetish of the original, while leaving yourself open to the question of why you bothered in the first place. Who, after all, needs a cheap imitation? If you make the song your own, you will still rile the fetishists, and you may or may not come up with something to compete with the original. Still if you do come up short, you will at least have failed on your own merits. The choice seems obvious; the only question is how far from the original should you stray.
For instance, in an interview on the Canadian talk show, Paul Simon was asked about why he chose Aretha Franklin's cover of "Bridge Over Troubled Water" for his new retrospective, Songwriter. His answer was that the singer's soulful rendition was as good as "Artie's." She didn't copy; she created. And she won a Grammy for it. The greatness of her performance was that she honored the song as a work of art with more than one possible interpretation.
ZZ Top: A Tribute from Friends is an album filled with the kinds of covers that honor the work of "that little old band from Texas" with performances that may not make you forget the originals, but still might have you saying they were as good as Frank's and Billy's and Dusty's. The "friends" featured on the disc are a mixed bunch of some of the finest on the contemporary scene and represent a wide range of musical genres from as far apart as Wyclef Jean and Jamey Johnson. And if Jean's "Rough Boy" may be a bit too mannered for some tastes, Johnson does a job on "La Grange" that is eight minutes of rocking power. He takes the song to another level. It probably didn't hurt that Billy Gibbons is sitting in with guitar and vocals.