The eventual successor to Azure Active Directory Synchronization Tool (DirSync) is the Azure Active Directory Synchronization Service, also known as AADSync. Although AADSync provides new features that DirSync does not, it also lacks a few features currently in DirSync, especially in the first GA version... So what exactly are the differences between the two?!
For a comparison chart of the features that each of these tools currently supports for synchronizing your directory with Azure Active Directory, visit the Directory Integration Tools webpage.