I needed a form builder for my site. After trying out several I settled on Ninja Forms. This plugin has one of the slickest user interfaces! Building a form is a breeze! The free version is very powerful & can serve the needs of most basic users. If you need something with more features, just browse their add-ons. They have something for every scenario you could ask for. Be sure to look at the bundles! They are cost effective & well packaged.
The only thing better than the plugin is their support! Their support is both responsive & thorough. They also see you through to the end. They don't just send an automated response & drop you. I had a few problems with my site (all user error). They were able to quickly get me back up & rolling. They also offered great tips on how to better achieve my goals. I wish there was a 6th star!