I would recommend the Microsoft Kinect SDK (most recent is 1.8), as it is the official SDK for Kinect, and has many different functions for interfacing with skeletons. However, I have to admit I have a bias as I have never used OpenNI or Open Kinect. You could try to use the Kinect SDK OpenNI bridge if you really wanted both, however that link does require version 1.5.
It is just simple math to calculate the angle between the joints, so your issue requires more thought as to what you are trying to accomplish otherwise and what you will need for that. See Official Kinect SDK vs. Open-source alternatives describing the differences between the SDK and OpenNI.