What is the best martial art that expresses the teachings of taoism?

Tai Chi, it is self-explanatory.

A martial art in and of itself can not teach the concept of Taoism, but any martial art can become an expression of Taoism.
A martial art can a catalyst for the zen like state of enlightenment through a phenomenological methodology.
And traditions of Taoism have many examples and accounts of this for study.
But an understanding of the philosophical goals of Taoism is not necessarily included in a given martial art or the goal of a particular martial arts instructor.

Since there are no offensive moves in the art, I would say Akido.

I am guessing. I think the manipulation of chi energy has to be one of the most mystical and downright incredible of things to accomplish. I saw a documentary on chi energy on television and it was fabulous. In China there are a handful of people who are masters of chi energy — according to the documentary. An old man was shown who is a master. He has students who attempt to wrestle with him. All younger men, including muscular and highly athletic men. A challenger approaches the old man and attempts to force him to the ground, or to just gain an advantage over him physically. The young men can not get any advantage over the master of chi. As one man said after wrestling with the man and failing, “I can’t affect him.” The journalist asked if he felt anything. “No,” he said. “I don’t feel any force or energy.” “I just can’t overpower him or affect him at all.”