@AliEtoom: There are advantages and disadvantages to both. While the Kinect SDK doesn't include built-in support for gestures, the SDK ships with a gesture sample ("Slideshows Gestures WPF" ), and several open source tools exist for building gestures like this one: http://kinecttoolbox.codeplex.com/
The 1.5 Kinect SDK includes several features not available in OpenNI/NITE, like seated skeletal tracking, face tracking and support for Kinect for Windows near mode. The SDK also includes lots of samples and helper classes to get you started, like UI controls for camera, depth, skeletal data, audio, and Kinect sensor management. With OpenNI/NITE, you have to do all of these things, like wire up the raw camera data, or skeletal joints yourself.