REST and GraphQL
Choose whether the Delivery endpoint or the GraphQL endpoint is most relevant for your use case. The Delivery endpoint is very convenient in giving you the full content from a page in the Pages app and a story from the Stories app with one simple call. On the other hand, if you need to retrieve content from a content app (a specialized app type for managing structured content, see Content Types) and you want control of exactly which properties and related content is included, GraphQL is most convenient.
You can use both in your project. REST Delivery and GraphQL are not competitors. Rather, they complement each other to provide you with the flexibility for discrete content retrieval scenarios.
For more information about the endpoints, see the following links:
Phil Sturgeon: GraphQL vs REST: Overview (snapshot at archive.org)