These lists are based on what, feedback from young employees that have never had another job in their life?
So big four employees believe they work at the best firm? What a surprise.
I work at a mid sized firm and they email surveys to see how everyone feels about the company. So these results go to a newspaper and we're seen as a certain rank as “top places to work for”. It's kinda B.S. They encourage you to be “honest” but really they want that accolade over anything.