Autoresponders were built for you to send a single email based on a contact's action. Mailchimp's newer marketing automation feature offers many more options, including the ability to schedule multiple emails based on many trigger activities. Although we strongly recommend you take advantage of this powerful tool, you can continue to use legacy autoresponders in your account.
Infusionsoft is a fully functional CRM and marketing solution created for small and medium-size businesses. Comparing it to Mailchimp or AWeber is like comparing a Lamborghini to a VW Golf. It provides highly advanced features for list segmentation, lead scoring, and marketing automation. On top of all that, you can integrate all of these features with your optin form using Infusionsoft Tags + OptinMonster.