When it comes to formatting URL's, I think it's important for the URL's to make as much sense as possible from a hierarchical stand point. Moz has a really good article on the optimal URL structure. So you can sort of think of the blog keyword as the subcategory keyword from the example in that article.
Further more, look at how both moz and Matt Cutts structure their blog URL's.
https://www.mattcutts.com/blog/seo-advice-url-canonicalization/
Hope that helps!