The general rule for building forms is that you should have as few fields as possible, as too many fields can lead to a drop in conversions. But you also have to avoid creating a form that doesn’t gather the information you need. This is where the conditional logic in WordPress form builders is so great -- your form can tailor itself to the exact needs of the person filling out the form.
If you’re looking for a powerful and free conditional logic from a WordPress form builder plugin, Caldera Forms is a great choice. Caldera Forms has a page builder-like drag-and-drop interface and an intuitive conditional logic system. As a free alternative to Gravity Forms and Ninja Forms, Caldera Forms conditional logic is a free feature.