Ask HN: Sending a reminder user activation email -Mandrill, Mailchimp or Marketo

When a user gets added to our app, we send them a user activation email via Mandrill. We want to send a reminder email 1 week after the first if they haven't activated their account. I want to just use Mandrill again, but some on my team think we should use Mailchimp in a scheduled/drip campaign, or Marketo using triggers. Is there any general knowledge or guidance about what kinds of emails should be sent through each type of system?