SEO: Subdomain or subdirectory for blog?

I cannot answer for SEO. But from my very different vantage point, I believe that

brand.tld/subdirectory/etc

outshines

subdirectory.brand.tld/etc

in terms of brand visibility. Remember, human beings as well as search engines will see your URL. It's not just a functional mapping; it's also a form of advertising.

Google claims they view these structures nearly the same way however In my opinion I see better authority given to the first example you cited and this is the structure we regularly use.

It doesn't matter like it used to.. or in a traditional SEO sense like you may be thinking. The most important thing now for SEO is to make sure that your blog is being promoted well and that it's an active part of your social media promotions along with your website.

That being said, if it's on topic then I would put it in a directory. This will increase the overall authority of your domain as long as you actively link from your blog posts to relevant pages throughout your website on a consistent basis.

I second Kyle's answer (just upvoted it) - and downvote any of the subdomain recommendations.

There is a running myth that subdomains hold the same SEO value as subdirectories... Unfortunately Google reps have confused a lot of people about this topic.

The subdomain option is only advisable if your site is an absolute beast. A good example of this is blog.HubSpot.com - their subdomain blog ranks really really well. However, they have a small army of marketers publishing, promoting, and sharing their content daily. They have also had several rounds of funding to fuel this authority they're gaining on the subdomain. Unless that sounds like you, avoid the subdomain strategy.

Compare that to the average blog, and it's a clear choice to use the directory over the subdomain, so you're not splitting authority across two domains. I don't care what Google has published, the data and the facts show time and time again that for 97%+ of blogs, subdirectories get much more SEO love than subdomains do. The reason is mechanical in nature. Think about it. Two domains equals twice the links necessary to get the same authority on one root domain. After optimizing hundreds of sites since 2005, I've found this to hold true with rare exception (the blogs that are beasts).

Follow respectable SEO's (like moz.com) who have case studies and data to show what's currently working on sites that are similar in size to yours. That's where you'll find the answer.

Its the same. But the smartest thing to do using subdomain or directory is to keep them as short as possible.

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."

Subdomains are neat. If you ask me, blog.bobtopia.com is more appealing than bobtopia.com/blog. But if we want to make an informed decision about the best strategy, where do we look? If we're interested in SEO, we ought to consult the Google Bot. Subdomains and subdirectories are equal in the eyes of the Google Bot, according to Google itself. This means that Alice and Bob have the same chance at ranking in search results. This is because Alice's root domain and Bob's subdomain build their own sets of keywords. Relevant keywords help your audience find your site in a search. There is one important caveat to point out for Bob: A subdomain is equal and distinct from a root domain. This means that a subdomain's keywords are treated separately from the root domain. What does this mean for Bob? Let us imagine bobtopia.com is already a popular online platform for folks named Bob to seek kinship with other Bobs. In this peculiar world, searches that rank for bobtopia.com would not automatically rank for blog.bobtopia.com because each domain has its own separate keywords. The lesson here is that keywords are diluted across subdomains. Each additional subdomain decreases the likelihood that any domain ranks in each search. A high-ranking subdomain does not imply your root domain ranks well. Subdomains also suffer from backlink dilution. A backlink is simply a hyperlink that points back to your site. Alice's attribution to a post on the etymology of Bob from blog.bobtopia.com does not help bobtopia.com because the subdomain is treated separate but equal from the root domain. If Bob used subdirectories instead, Bob's blog posts would feed the authority of bobtopia.com and Bobs everywhere would rejoice. Although search engines have improved at identifying subdomains and attributing keywords back to the root domain, they still have a long way to go. A prudent marketer would avoid risk by assuming search engines will always be bad at cataloguing subdomains. So, when would you want to use subdomains? A good use case is for companies who are interested in expanding into foreign markets. Pretend bobtopia.com is an American company whose website is in English. Their English keywords will not rank well in German searches, so they translate their site into German to begin building new keywords on deutsch.bobtopia.com. Other use cases for subdomains include product stratification (think global brands with presence across many markets) and corporate internal tools (think productivity and organization tools that are not user facing). But unless you are a huge corporation or just finished your Series C round of funding, sub domaining your site into many silos is not helping your SEO.
If you are a start-up or small business looking to optimize your SEO, consider subdirectories over subdomains. Boosting the authority of your root domain should be a universal goal of any organization. The subdirectory strategy concentrates your keywords onto a single domain while the subdomain strategy spreads your keywords across multiple distinct domains. In a word, the subdirectory strategy results in better root domain authority. Higher domain authority leads to better search rankings which translates to more engagement.
Besides if you do have any questions give me a call: https://clarity.fm/joy-brotonath