Azure is the more common of the two in our index: it runs on 3,323 websites against 395 for Acquia Cloud Platform, and 26 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.
Azure is a cloud computing service for building, testing, deploying, and managing applications and services through Microsoft-managed data centers.
Within the paas sites we have indexed, Acquia Cloud Platform holds 0.9% and Azure 7.7%.
26 sites run both Acquia Cloud Platform and Azure. That is 7% 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.