Quick answer - the best educational baby toy, especially for a 0-6 month old, is.... YOU! :-)
Babies at that young age don't really need 'toys' - they need interaction. Someone to hold them, someone to talk with them, someone to take care of their needs in a comforting way.
Once they get closer to six months old, it's nice for them to have objects to reach for and to practice grabbing & holding, but an empty toilet paper roll or a kitchen serving spoon or that random mate-less sock from the dryer is just as good as any 'educational toy' you can buy.