If your website is mostly words and the people who read them, these two are the shortlist. They solve the same problem and charge for it in opposite ways, which is what makes the decision unusually clean.
How each one gets paid
Substack costs nothing to publish. There is no plan at any size — the platform takes a tenth of every paid subscription, permanently, on top of the payment processor's fee, and a custom domain is a single one-time charge. Nothing is owed until readers start paying, and once they do the bill scales with success and never stops.
Ghost charges a subscription and takes no share of your revenue. That means real money before the first subscriber, and a cost that stops growing once you are established.
The crossover is arithmetic rather than judgement. A publication earning very little is better off where nothing is owed. A publication earning steadily hands over more in revenue share than a subscription would ever have cost, and the gap widens every month.
What you can do with the site
Ghost gives more of a website. Themes are replaceable, the content model is real, and the published result can be moved elsewhere because the software is open and the export is meaningful.
Substack gives you a publication that looks like Substack. There are pages beyond the posts — an about page and others sit in the navigation — but design control is close to absent, and that is the deliberate trade for the writing being the product rather than the layout. A custom domain does attach, so the address is yours even when the appearance is not.
Which should you choose?
Choose Substack if you are starting, you do not know whether anyone will pay, and you would rather owe nothing until they do. Accept that the design is not yours and the cut is permanent.
Choose Ghost if the publication is already earning, or you want the site to look like your business rather than a platform, or leaving one day matters to you. Price it against ten per cent of what you expect to make, not against zero.
Substack
Owes you nothing until readers start paying for what you write.

Ghost
Writes for a business whose website is mostly writing and an email list.
Specs
Ratings
Ease for a beginner
Design and templates
Room to grow
Help when you are stuck
Value for money
Features
Pricing
Substack
Ghost