When comparing these two products, the main differences that stand out are plan limits and overall design philosophy. Their feature sets are comparable.
Formspark is the only competitor of Submit JSON that is not subscription based. They offer a single plan, a one time $50 purchase for submissions.
Regardless, it's another Formspree clone. Formspark's HTML-first approach is misguided and insecure.
In comparison, Submit JSON's API-first approach is more versitile, secure, 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.