When do you choose Spring MVC versus Spring WebFlux?

I inventory every database, HTTP, file, and library boundary before selecting or migrating the stack. A bounded scheduler can isolate unavoidable blocking calls, but extensive isolation often means MVC is the more honest model. I compare throughput, tail latency, memory, thread behavior, cancellation, and operational skill under representative load rather than relying on a reactive label. A mixed estate is acceptable when each service has a coherent model; mixing blocking and reactive styles casually inside one request path is harder to reason about.