196511 sites use the very well established Webforms module - so it has been a very popular module for some time. However, in some ways, it is getting a bit long in the tooth now, especially with some of the new features available in Drupal 7, such as Rules integration. So along comes a new upstart, Entityforms. This brings the webform functionality into standard use of the Drupal 7 field API, and is based on the well-respected Model Entities example project.
The big advantage is that it automatically exposes the Entity forms (which are themselves entities) to Views, Rules, etc. - so can benefit from all the best new features of Drupal 7.
It's still in it's early days, of course, but seems to work well out of the box.