How do you decide between using a Flow, Process Builder (retiring), or Apex for automation?

Salesforce's automation strategy prioritises Flow Builder as the single declarative automation tool. Decision framework:
Use Flow Builder (preferred declarative tool):
— Record-triggered flows replace all workflow rules and most Process Builder use cases.
— Screen flows replace custom VF pages for guided user processes.
— Scheduled flows replace time-based workflow actions and batch Apex for simple field updates.
— Auto-launched flows replace simple Apex called from other processes.
Process Builder (retiring): Salesforce has announced eventual retirement. Migrate all Process Builder processes to Flows before they are sunset. No new Process Builder development should be started.
Workflow Rules (retired): Already retired in 2023. All existing workflow rules should be migrated to Flows.
Use Apex when:
— Complex looping logic, data structures (Maps, Sets, nested collections) exceed Flow capabilities.
— Callouts to external systems with complex authentication or response parsing.
— Batch processing of millions of records (Batch Apex).
— Unit-testable, version-controlled code is required for compliance.
— Performance-critical paths where Flow overhead is measurable.
The App Builder certification expects knowledge of the declarative approach — Apex questions are outside the scope of the certification exam.