diligent, the link I supplied goes into more detail, but in short it was a survey by The Age.
Interestingly the claims about Gillard being the worst PM is similar to the claims previously made against Howard at the time of being the worse PM.
Below is one example which you could easily swap Howard's name to Gillard's. I'm guessing the next PM could run into similar claims down the track as well.
So are the claims factual or political?
Our worst PM
Eleven years under John Howard saw needless deaths, distrust, and divisiveness. A relentless turning back of the clock has occurred and may never be corrected. The Howard regime has produced in many parts of the nation a sense of bitterness and betrayal, with cherished values discarded.