When comparing these two products, the main differences that stand out are included features and overall design approach. The cost of Web3Forms and Submit JSON is compareable.
If you're receiving less than 2,500 submissions per month, Submit JSON is a better deal than Web3Forms. Otherwise, Web3Forms comes out on top there.
Web3Forms does not store your submissions though, that's why it's so cheap! Their feature offering is lacking compared to Submit JSON as well.
Hate to say it, but Web3Forms is another Formspree clone, albeit a much more affordable one! They fall short where Formspree falls short. But if you are gung-ho on HTML only submissions, we think this is the best choice of the bunch.
In comparison, Submit JSON's API-first approach is more secure, versitile, and aligned with modern web development best practices.
Which is the best form backend for you? We think the answer is obvious, but we'll let you decide.