If you want a simple contact form where users can contact the website administrator or something that Contact Form 7 is the plugin for you. Formidable Forms will do the job too, but using it for a simple contact form would be like using an atomic fly swatter. I talked about Formidable forms in another article, this is a different and simpler use case.
Contact Form 7 is not good for conditional logic or doing anything fany with entries to a form, I have personally found this plugin useful only in the simplest of cases. If you need an easy way for users of your site to get in touch with you and you do not want them to follow specific rules with the message then Contact Form 7 is the plugin for you.