I like the framing that this isn't really a "LangChain vs LangGraph" decision it's a control flow decision. A good rule of thumb is to start with the simplest abstraction that fits. If your workflow is deterministic, a chain is easier to build, debug, and maintain. The moment you introduce retries, conditional routing, or multiple agents making decisions, you've crossed into orchestration territory, and that's where LangGraph starts earning its complexity. Choosing based on workflow complexity instead of tooling trends usually leads to much cleaner systems.