There are currently three different apps that are all pretty similar despite their titles. All versions have the same board layout, letter count, powerups, and rules. However, there is one app that seems to be slightly prioritized than the others. This one is Words With Friends 2 which is the most recent version from Zynga. This is the best Words With Friends app because it is usually updated before the other ones. So you have the chance to get access to the newest features and improvements before the previous versions.