One thing I like most about MailChimp is it has a free pricing option whereas AWeber has $1 option as a starting point. That means you can create a free account on MailChimp without giving your credit card details whereas you need to pay $1 for first month to start using AWeber. You can try AWeber by just paying $1 for first month. After that, you need to pay $19 each month.
One of the best features of AWeber is the ability to create a series of emails that are automatically sent out to new subscribers. This allows you to create an eCourse or some sort of introductory guide for your latest subscribers. This is fantastic as you can market it as an incentive for people to subscribe (e.g. subscribe and get our free 7 day eCourse) and once setup, you can leave it to be sent out automatically.
Even if you've imported an existing list of contacts, you'll still want an easy way for new fans to join your email list. AWeber's sign up forms provide the perfect solution. Create a simple sign up form for your website, and if you don't have a site, we'll host it for you. Grab the link to your AWeber form and share it on Facebook, Twitter, LinkedIn, or wherever your audience is.