Should my banners link directly to a sales page or to a landing page?

If I have a blog, or a tumblr, or a website or something with banners promoting an affiliate product, would it be best to send the banner clickers to a review landing page, or straight to the sales page?

Depends on your product, audience and other factors. If you are not sure there is one way to find out indefinitely, research "split testing" or "A/B testing".

Good luck!