Amazon Web Services is the more common of the two in our index: it runs on 34,724 websites against 395 for Acquia Cloud Platform, and 395 sites use both. Counts come from real scans of each site's home page, not vendor claims, and cover the sites in TechLookup's index rather than the whole web.
Acquia Cloud Platform is a Drupal-tuned application lifecycle management suite with an infrastructure to support Drupal deployment workflow processes.
Amazon Web Services (AWS) is a comprehensive cloud services platform offering compute power, database storage, content delivery and other functionality.
Within the paas sites we have indexed, Acquia Cloud Platform holds 0.9% and Amazon Web Services 81%.
395 sites run both Acquia Cloud Platform and Amazon Web Services. That is 100% of the sites using Acquia Cloud Platform, the smaller of the two.
Want to know which one a particular site uses? Look it up and see its whole stack, or compare two sites side by side.