What do I USE? Honestly - MY WIFE.
What did SHE use? a combination of all the above - WD-40 or Goof-Off, a soft cloth, finger nails, hair dryer.
The hair dryer softens the glue, you peel what you can, if it not coming off soak it with the WD or Goof-Off, use that and some heat and the cloth.
I'm told they're really a bitch to remove, but they met their match in Jenn. 
I'd be afraid that Goof-Off might damage the paint.
I've used heat to loosen, then peal, and then WD40 for the residue with success many times.
Jenn is a better sport then my wife, who said, "get Jenn to do it" when I told her that she removed Kev's stickers.
