When comparing Substance vs Gatsby JS, the Slant community recommends Gatsby JS for most people. In the question“What are the best solutions for a personal blog?” Gatsby JS is ranked 9th while Substance is ranked 23rd.
Ranked in these QuestionsQuestion Ranking
Pro Free for one site
One site is free, for other option see pricing.
Pro Easy importing of Jekyll posts
An easy to use interface for migrating from Jekyll is available.
Pro Clean and simple layouts
Substance doesn't clutter your blog, it gets out of the way so people can focus on reading.
Pro No page reload when navigating
Pro Based on React.js
Editing markup is phenomenally easy when you have components.
Pro A lot of plugins
Gatsby offers a lot of plugins to integrate tools like SASS, typescript, styled components, etc.
Pro Live reload
Every change you make can be almost immediately seen in a browser.
Pro Open Source
Pro Take content from any source
Gatsby can generate the pages with content from any sources like Drupal, Wordpress, Contentful, etc. If the source plugin is not coded for your solution, you can create it.
Pro A static site and a React app in one
The static pages are generated by Server Site Rendering of the React app. So you have all benefits of a static site, and all benefits of a React app, which is very powerful.
Pro GraphQL Data Layer
Pro A lot of examples
Gatsby have a lot of examples sites in his github repository.
Pro Very active development
Gatsby is very actively developed and the maintainers are very helpful.
Pro Beautiful out-of-the-box blog starters
Pro Built-in code and data splitting
Con A bit raw
You'll maybe have to tweak some JSX if you want something that's not covered by available themes.