As far as I'm concerned Tai Chi is more of a spiritual stuff, energies in a body etc. Surely it burns calories, but I wouldn't count on it in a moment of self defence. Slo-mo may look cool, but... Tae Kwon Do on the other hand is a traditional martial art and involves lots of kicking. So, you have to decide between a Bruce Lee style *** kicking action and calm meditative concentrating.