In Amazon Neptune, both RDF graphs and Property Graphs are stored in a “quad” representation using a custom data model. They can be accessed as a property graph or as an RDF graph.
Neptune offers a number of reasons to choose it over other graph databases. The most prominent are its scalability and high availability (enabled by its read replica driven storage architecture), its relative affordability (a T3 instance in Neptune is under $0.10/Hr.), and its compatibility with both property graph and RDF graph query languages.