Registrationmagic is one of the best options for registration forms for WordPress, with a plethora of features that allow you to create custom registration forms for any purpose, and add them anywhere on the site using a shortcode or widget. And most importantly: it allows you to have total control over user registration information, as well as offering various extensions and external integrations. For example, WooCommerce, MailChimp, Dropbox, user registration forms with front-end login (Facebook, LinkedIn, Microsoft, Twitter, Instagram, and Google), payment systems, analytics, and reporting, among many others. Even in the free version, it already offers a large number of features.
It is the most comprehensive registration form plugin available for WordPress in the premium version.