I would rather “stay sharp” than “stay fresh”. My logic behind this is staying sharp means you keep a figurative “cutting edge” and are ready to “cut” when needed. Also, the opposite of sharp is dull which is useless when you need a cutting edge. Now, as for “staying fresh”, it implies that you are keeping yourself fresh and ripe for the plucking or consumption. In other words, ready to be devoured. I would rather be a sharp edged sword than a fresh pie. Just a thought.