Capybara I'm not sure what you mean by "cardinal"? The 2 extensions are completely different implementations of a similar concept. Many use cases can be achieved with either of them.
Formulaire offers more field types (in particular, lists and file uploads) and has more permissions around the visibility and edit abilities. Formulaire can also integrate with the sign up form.
The only thing I can think of that Masquerade does differently than Formulaire is the ability to search users by form answers with the native MySQL search driver. Formulaire also supports search, but only with the Scout integration. Scout is much better if this is something you plan to use regularly.
Both extensions can be used at the same time, though it probably doesn't make a lot of sense.
If you have a use case in mind, feel free to share, I might be able to give better suggestions.