Either one will work and it is going to depend on the preferences of the developer. There was a question about this on Stack Overflow, where the developer for Spring Cloud Gateway pointed out that Zuul will not be integrated into Spring directly, so Spring Cloud Gateway would likely be easier to work with: https://stackoverflow.com/a/47094859/11002318
Configurations of Azure Spring Cloud Sample PetClinic
Azure Spring Cloud Sample application PetClinic below put configurations at two places
https://github.com/Azure-Samples/spring-petclinic-microservices
For example, spring-petclinic-api-gateway application has application.yml at spring-petclinic-microservices/spring-petclinic-api-gateway/src/main/resources/ which uses Spring Cloud Gateway for Routing,
but configuration server load configurations api-gateway.yml from git repository at https://github.com/Azure-Samples/spring-petclinic-microservices-config/blob/master/ which uses Netflix Zuul Gateway for Routing.
It is quite confusing. Which one actually effective?