When you go with AWeber, you get the complete email managerial package. Simply, opt-in forms are available to embed in your website, which AWeber used to collect subscriber details. You can send out fully customizable emails manually or on an automated schedule. AWeber further allows you to segment your subscriber list down by subscriber behavior and even target content, allowing you to choose who gets what, and when. Tailoring your content to fit your subscribers is basically a gauranteed way to increase your views and subscriber base and conversion rates.
AWeber provides a simple interface which is easy to manage, and they also provide a large array of tutorials to help make the learning process a bit easier. The templates they provide are also of grat value as well. Tracking subscriber behavior and data is a huge bonus to help improve your conversions. A free 30-day trial is always a huge bonus as well.
A little more expensive than the alternatives. Template quality leaves a little to be desired as well, and the inability to send video via email seems like an outdated issue that should have been solved a long time ago.
Because it's basically the Industry Standard
If you don't mind spending a little more, AWeber is currently the go-to for email list/subscriber management. Fast support, years of de-facto experience as a provider and a 30-day trial make AWeber hard to say no to!