The best wordpress thmees are the search engine friendly ones. Not all wordpress thmees are search engines friendly. Of course only thmees won't give you traffics, but thmees are also important factor. Don't look for how cool theme are, but look for search engines friendly one. As i am aware of, thesis theme is very popular of it's SEO opmtimization, however there are some free thmees that created by thesis creators too, here are some list: