Tai chi more effective than yoga?

A colleague pointed out this interesting article in the Times of India comparing yoga and tai chi. I have always found the problem with overstretching when I have done yoga. With tai chi I think it is partly that the focus of teaching is more on stretching exactly the right amount rather than encouraging the belief that the more you stretch the better you are doing. However, I think the moves themselves are more geared towards things that the body normally does, which is why people often feel that they are not doing exercise when doing tai chi, until they feel the benefits afterwards.