What is the best email newsletter subscription plugin for WordPress?

I have been using FreshMail Newsletter Forms for WordPress since a year. It's very good plugin allowing you to do a lot with subscription form:

• - Define popup style by choosing predefined templates or creating your own in WYSIWYG editor.
• - Include sign up forms in popups and define when it will be displayed.
• - Set up automatic subscription sign up with checkboxes added to various wordpress forms (for example to adding comment form).
• - Get reports on the sources of users' registration and check which form or generates the most new subscribers.