The question that actually separates them
Ask one thing of any form plugin: does a submission get written to the site, or does it only become an email? Gravity Forms and Ninja Forms store every entry in the database. Contact Form 7 stores nothing at all. WPForms depends on your licence tier. That single answer decides whether a failed email is an inconvenience you can recover from or an enquiry that no longer exists, and it matters far more than which builder interface you prefer.