Migration can actually be a major pain in the ass. Although according to aWeber my list was “substantially clean” but I still needed to get all my readers to reconfirm their subscriptions. After a week I’m still waiting for 70% of them to reconfirm. NOT happy. If I stuck to mailchimp I wouldn’t have had these problems. (Their support guys are good though.)

I’ve worked with Promote Labs now for over 11 years. Year after year Jeremy and Simon have landed at the top of my leaderboards for Internet Marketing products with a strong emphasis on Video Marketing. These are VERY competitive leaderboards with sales hitting both six and seven figures. The additional effort that they put into… “Solid Killer Promotions Year After Year”
AWeber finds a healthy balance between ease of use and robust functionality. There are some nice features — particularly in the autoresponder realm — but navigation is intuitive enough that I was able to perform basic tasks without looking up tutorials. When I did find myself at a loss and turned to the online help resources, I was quite impressed with the range and scope of guidance available.
Alex GetResponse is a good service too. They have a smaller customer base than MailChimp or Aweber but they are definitely on the right track. You should consider your own options that will help you decide. For example, pricing, growth, support, reliability, deliverability, spam filters, etc. Make a list of these factors to compare on your own, you will also find such analysis around the web but those analysis could be biased towards one of the service. So you better do it on your own.
So, when a new person signs up to your site (via your newly created signup box), they will (after confirming their subscription) start to receive the set of emails that you have setup.  You can create as many as you want and schedule them to be sent out at different intervals (i.e. 1 a day, 1 a week, 1 a day and then another one in a month’s time, etc.).
As with most ESPs, you’ll need to certify that any list you upload is permission-based and conforms with the provider’s anti-spam policies. AWeber takes this a step farther than some. You will need to enter the source of the email list when you upload it, and AWeber requires confirmed opt-in for all addresses. This means your first email will have to be a request for your subscribers to confirm their subscriptions. Anyone who doesn’t confirm can’t be on your list. (AWeber does allow some exceptions to this rule if you have a list that has already gone through confirmed opt-in with another ESP.)
4. Affordable: I was willing to pay more money for better features, but wasn’t convinced I needed to be paying $200-$300/month for those. I know many, many, entrepreneurs who pay those fees and like I say above, use a fraction of its capabilities. I didn’t feel that was necessary for my business – at the point of consideration, I didn’t have a complex business with numerous products or sales funnels. For the past couple of years while my kids are home on crazy-small school schedules (right now I have 2.5 hours per day), I have been primarily working 1:1 with clients and offering My PRO Plan. This will change in Fall 2016 when both kids are in school full time (I can’t even imagine!?!) and I have more time to execute on my ideas, but for now, the big shot services weren’t needed.

To start, you’ll have 700+ templates to choose from. There are some very nice layout customization options here, once you learn how to use them. AWeber uses both “sections” and “blocks” in its organization. Blocks are elements like text boxes, images, etc. Sections are the frameworks in which they exist. Most programs use similar organization, though they may use different terminology. The difference comes in your ability to edit or customize the sections themselves. In previous versions, the ability to customize elements like buttons was limited–you couldn’t change the text of buttons–but you now have the ability to easily customize those elements.
Think about implementing referral links to incentivize your subscribers to spread awareness about your brand, too. Referral links allow your current customers to promote trackable links for your business. In exchange for sending new paying customers your way, you can give them incentives like discounts, coupons, vouchers, cash, prizes or redeemable points.