Contact Form 7 really is one of the best contact form plugins out there. The code is well written, and it is reliable. We've used it since it's early days....it probably was 2007 or 2008.

We use it to power a number of different types of forms on both our sites and client sites. It may not have as many of the visual bells and whistles as say Gravity Forms, but it is pretty lightweight in code and overhead for what it does, and it hasn't had any major security issues in a couple years, which is saying a lot, considering how many people use it.

We do use other form plugins when we need more features, so we do like Gravity and Ninja as well, but CF7 is definitely our go-to.

Kudos to Takayuki for the good work on this plugin over the years!