The one you will find in stores now, made by Avalon Hill is the revised map, with some rule changes. Arguably, a more difficult game due to additional pieces, more territories, and greater options for strategies, etc.
The older version (the Milton Bradley one) is the classic, and has a nice sized game board. If you have never played before, the older version is easier to learn on.
Personally, I am just hoping for a PC version of Revised and the D-Day/Pacific variants with some really good AI in the near future :-)