After reading over my first prompt regarding Strunk and White I remembered why I liked their book so much. Williams book, "Style: Toward Clarity and Grace" is a style book from a whole different genre almost.
Strunk and White use clear, to the point examples that are short and easy to understand. Williams used paragraph examples that truthfully, kind of lost me because of their depth. Strunk and White is an easy reference guide while Williams is a better learning guide because it goes into more depth.
Williams advice is more useful for long term, I think. So, if you wanted to learn something and memorized his discussions and examples you would know it to a greater degree than you would if you attempted to learn the same thing from Strunk and White. Williams writes for Professionals; Strunk and White wrote for students.
Williams didn't just tell us how to write he went ahead and explained why it was better the correct way than the wrong way. Strunk and White did not do that, but I still appreciate their book and their writing advice.