RSForm!Pro has been around for quite some time, the first release being in 2009, and it's been fairly consistently updated since then. With 1.4 million downloads from the Joomla extension directory, it's also one of the most widely used.
They offer plenty of features, including, but not limited to:
Multi language support - use the same form for multiple languages.
GDPR support - you'll be able to easily build GDPR compliant forms.
Built in Grid System - build your forms on a grid with drag and drop functionality.
Multi-Page Forms - split your form over multiple steps if the information you need to collect is too complex or detailed to easily use in a single page.
AJAX Validations - validate your form fields over AJAX to provide real time updates to your users.
Spam protection - the extension comes with two different image Captcha challenges, along with an invisible Captcha, to prevent spam form submissions.
Form Response Export - to Excel, CSV, PDF or XML.
Multiple Themes - including Bootstrap 2-4 and UIkit
There is a free version of RSForm! available on the Joomla Extension Directory, the premium license comes in three versions - either a single or unlimited websites, the unlimited license is available as either a six or twelve month subscription.
Additional fields and payment plugins are available as separate options when you buy a subscription.
RSForm!Pro is a must have for all web developers. With the full set of features available you can easily create the most elaborate forms for your website, starting from simple contact forms to advanced multi-page forms with dynamic content.