The Best URL Permalink Structure

I have recently changed my permalink structure from

/%postname%/ TO /%year%/%postname%/

It was after experiencing slowdown in the server. It was recommended by wordpress to use atleast 2 levels of permalink structure like /article/%postname%/ or /%year%/%month%/%postname%/.

Another controversial recommendation is using this permalink: /%post_id%/%postname%/.

My question is:

What’s the best permalink structure with regards to wordpress performance?