I would say they both aim for more-or-less the same thing: purification of the energy body. But tai chi places real emphasis o grounding, while Yoga can be a very super-powered blow-your-brains-out-ecstasy regardless-of-the-consequences practice. You will really want the groundedness that tai chi offers even if you decide to do yoga as your main practice.
My recommendation from my short personal experience: do tai chi. Yoga you can do later when you know tai chi