I like the look of “posts” - but want to make sure I stay in proper guidelines when creating a blog. So, that being said… for proper SEO, should the URL end in “blog” or “posts”.
i would prefer “blog”, because it is clearer for the user that all pages coming to “…/blog/…” belong there.
Only “posts” seems very generic and unspecific for the user.
Maybe sometime in the future it will be possible to add a folder Slug for Collection Pages, so that you can use “…blog/posts/your-blog-post”.
And never forget, SEO is not everything, but everything that does for the user is good for SEO.