Tom wrote me the other day:
[For SEO,] would you recommend me starting a blog via the: 1) Shopify Blog feature? or 2) On a WordPress Site?
I have heard that WordPress have better SEO. TBH I think Shopify is pretty good (but I have absolutely no idea!).
WordPress has better SEO because of it's default settings and supply of themes that have a lot of SEO features built-in.
A Shopify powered blog could be just as good if the blog templates in your theme are coded well.
The biggest issue is that if you use WordPress, you'd need to put it on a different domain (e.g. blog.example.com) which Google treats like a completely different website. You'd get a better SEO boost by using the same domain (which means using Shopify).
But 80% of the value in a blog is the content. If you do that well, it won't matter if you use WordPress, Shopify, Blogger, or hand-coded HTML files with black text on a white background.
My Blogging Solutions for Shopify article has more details and recommendations about how to use a blog with your store.
Whatever you use, make sure you can get high-quality structured data on your blog articles.
Competition can be tough but if Google does award you with Article Rich Results, they can be pulled up to the #0 rank above all of the organic results.
JSON-LD for SEO automatically adds the data Google requires for Article Rich Results but only if you use it on your Shopify store.