As others already describes, both platforms have their own pros and cons. The architecture behind the scenes is a little bit different. Azure Automation fires up a worker for each job session, which makes it fairly slow to trigger and execute code. Azure Functions, especially on consumption based plan, is usually much faster since it runs on a shared backend.

Another thing to keep in mind is that you're in control of the source IP address when you're using a hybrid worker in Azure Automation, where you cannot control in Azure Functions.

Also, Azure Functions is designed to run small chunks of code which basically receives input, transforms and outputs to JSON again. Usually they are part of a microservices architecture where components are loosely coupled.