Google doesn’t care which you use, but be consistent when creating urls for your site. They are considered equal in terms of site rank and performance, but they are also considered different urls. If you’re not consistent you’ll split your traffic between the two versions and that’s generally bad for reporting and analytics if that matters to you.
Just remember to be consistent whichever you choose. You can do this manually or use the common practice of .htaccess redirects to ensure all appropriate links either include or exclude the “trailing slash”.