What is the best Email notification module?

There is so much information on this but it is quite confusing to dig through for a newbie.

We would like functionality that would allow a user to "subscribe" to a forum and have an email sent when a change is made to the forum. The user could select an immediate email or a summary email of all changes once daily. A user should be able to sign up for notifications without posting to the forum. Any change in content to the forum would cause a notification email to be sent.

We are currently using Drupal 6.2. Any suggestions would be greatly appreciated.

Thanks very much!