I have played in several published A/D&D game worlds from the Forgotten Realms, Greyhawk, Krynn, and Mystara. The list would be much longer if I included the many homebrew worlds but I am not considering those for this post. I would say that my favorite D&D game world is Mystara because of all the time my buddies and I spent playing in that world when we were young and would often sneak in all night gaming episodes while our parents were sleeping. I would like to see Mystara used in some official update by Wizards of the Coast. I have not kept up with D&D Next as well as I could have but I think Mystara would be a great fit for the Basic Rules module or whatever they are calling it in the end.