There has been a good amount of discussion about this, and a lot of studies show the subdirectory is the way to go, so go with that if possible.

The debate is summed up in total by this discussion between the Founder of Moz and Founder of HubSpot: https://inbound.org/blog/the-sub-domain-vs-sub-directory-seo-debate-explained-in-one-flow-chart

The golden summary: "Subdirectories are better for SEO. But don't let getting technical details right stop you from investing in blogging or content creation, because a blog on a subdomain is still better than no blog at all."