Oh, I prefer Del McCoury's bluegrass cover of "1952 Vincent Black Lightning."

Fightin' words!

Here's a few off the top of my head:

Dinosaur Jr's "Just Like Heaven" is beloved by Robert Smith because it is awesome.
Mike Watt's "Big Train" is better than the Kinman brothers' version.
There's no better version of "The Red And The Black" than fIREHOSE's, and that includes BOC's original and the Minutemen's version.
Any song that Jerry Lee Lewis performs is by definition better than the original.
Any Daniel Johnston song performed by another artist is also better than the original, especially if that artist is Kathy McCarthy or Vic Chesnutt.

Joe Cocker's A Little Help From My Friends is pretty damn wonderful.

OTOH, Witney Houston's Greatest Love of All is a sappy mess compared to George Benson's which it went and drove off my radio...

Blue Cheer's version of Summertime Blues. Husker Du's version of 8 Miles High may not be better than the original, but it's at least its equal.

Janis Joplin's "Summertime."

Whereas Hüsker Dü's version of Love Is All Around is far superior to the original.

The Jane's Addiction cover of the Dead's "Ripple" is one of my favorite things ever.

Lucero's cover of Jawbreaker's "Kiss The Bottle".

Siouxsie's cover of "Trust In Me".

Hank Williams III's "Atlantic City"

runs away.

Janis Joplin's "Summertime."

What are you thinking of as the original? It's probably better than whoever was in the original cast recording, but better than Ella? I dunno...

I've been learning Summertime for the theremin, so it's been on my mind a lot lately. :)

Whereas Hüsker Dü's version of Love Is All Around is far superior to the original.

Hard to argue with that!