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.
Under #2, be careful with popups or modals that cover other interactions, Google will now penalize this kind of activity on mobile. I suspect we’ll now see persistent banner style replacements on mobile (a strip across the top of the site that doesn’t scroll off the page or disappear until you close it or sufficient time has elapsed without interaction.)