I use the Zeiss and love it, great lens. I would worry shooting live with the 1.2 as it is hard enough with the 1.4 wide open trying to focus. The Zeiss is also smaller and lighter.
I've used the Canon 1.2 a little and it's an incredible lens. They used it a lot on the "House" episode in the "collapsed building" set with the 5D. However, for live events, it might be very difficult to focus it at f1.2. If it's fairly dark though, you might be cursing yourself for not having the extra light available.