Engineers designing big data processing for the first time typically start by asking, "Which service should we use? EMR? Glue? Athena?" But these three aren't competitors—they're the same engine (Apache Spark) wrapped in different operational models. EMR lets you directly operate Spark as a cluster; Glue abstracts Spark serverlessly; Athena exposes only SQL on top of Spark/Presto. So the real question becomes: "How much direct control of the cluster does this workload need, and how much operational burden are we willing to offload to AWS?"