When comparing these two products, the main differences that stand out are cost, plan limits, and overall design philosophy. Their feature offerings are pretty similar.
Basin's starter plan starts at $4/month with 250 submissions and 3 forms. Compare that to Submit JSON's $5/month plan that has a submission limit of 2,500 with 10 forms. Submit JSON's plans offer 10 times (1000%) the submissions on average with a comparable feature set.
Basin comes with a few bells and whistles that Submit JSON will not ever have, like a form builder. It's definitely targeted more towards non-technical folks.
Regardless, it's another Formspree clone. Basin's HTML-first approach is their greatest strength, and also their greatest weakness.
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.