Whats your favorite exercise to work your core?

I know this is more than just one exercise, but have you all tried the new Les Mills Program CXWORX? It is a 30 min workout in a Group Fitness setting or a small group PT session. CXWORX really hones in on the torso and sling muscles that connect your upper body to your lower body. If you haven’t heard of it yet, check this out…. http://www.getcx30.com/