I’m using Ninja Forms for the Contact Form on the Contact Page here – http://demo.appfinite.net/ambition/contact/ And I’m using the Genesis eNews for the Newsletter on the homepage. You can use either one, or both.
The Ninja Forms definitely has more options available than the Genesis eNews plugin overall, so it would probably be better to continue using it if you like it. If you don’t need it, and you’re already using a Contact Form, then you can use the eNews plugin. It’s up to you though, both will work fine.