WP Permalinks - /%postname% vs /%category%/%postname%

Unfortunatelly there is no absolute answer to your question.

Before I give you my take on it though I want to make it clear that I am not an SEO expert.

With that out of the way, here is what I think based on my own experience and on what I have read about the subject.

For micro niche blogs targetting small and tight niches, I would use only "/%postname%" (without the quotes of course).

On larger blogs it is good practice to organize the content under specific categories to make it easy for readers to navigate and to minimize the chances of your blogs being considered autoblogs by the search engines. In this case I would use "/%category%/%postname%".

Which is best for SEO?

Generally speaking, the shorter the URL, the better it is for SEO purposes.

However, I have read different opinions from webmasters that have used/tested both. Some say that using only "/%postname%" gave them the best SERPs results, where others claim to have better results when using "/%category%/%postname%".

Because results seem to be different for different webmasters, you will have to test both for yourself to see what works best for your own blogs.

I hope that this helps.

Tony Alves