The difference is in the WinDBG versions, specifically in the versions of the included debugging extensions and automation. Unless you have good reason, it's always best to install the latest version, which should be from the Windows 8 WDK or SDK. If you're not doing driver development and just need the debugging tools, Microsoft recommends using the installation package from the SDK:
[h=2]Install Debugging Tools for Windows as a Standalone Component[/h]If you don’t need an entire kit (neither WDK nor Windows SDK) but you do need only the Debugging tools, you can install the Debugging Tools as a standalone component from the Windows SDK. In the Windows SDK installation wizard, click through a few screens, select Debugging Tools for Windows on the page for selecting features/options and clear other components that you don’t want. This will download Debugging Tools for Windows without the rest of the Windows SDK.
