AEM as a Cloud Service will be the standard for experience management by Adobe for the next years.
The product was released at the end of 2019. Now (March 2021), there are minor differences between AEM as a Cloud Service and AEM On-Premise or AEM Managed Services.
For the moment, complex scenarios might be more challenging to deploy with AEM as a Cloud Service.
However, AEM as a Cloud Service will be able to manage any use cases, websites and integrations in the midterm.
What features are not supported in AEM as a Cloud Service yet?
The list of features not supported in AEM as a Cloud Service (May 2021):
The Classic UI is no longer available in AEM as a Cloud Service
Developer Mode in Page Editor
AEM Sites, Assets, Screens and Forms are already available for the cloud and constitute the core features of Adobe Experience Manager.
If you are doing e-commerce, AEM Commerce is as well available. To get started, your Experience Manager Cloud Service needs to be provisioned with the Commerce Integration Framework (CIF) add-on. The CIF add-on is an additional module on top of AEM Sites.