301 redirection is permanent redirection, whereas 302 is temporary redirect. As far as SEO is concerned 301 redirect passes all the SEO juice from the older link to new link. If you are changing the blog post URL, then 301 redirect is the best is SEO friendly bet. 302 redirect, whereas on the other hand, passes the SEO juice partially to the newer link. 301 redirecting the link with high authority, to that of another link, acts as high quality backlink to the new link. So the 301 redirect is preferred over 302 redirect.