The differences are explained in the JAX-RS specification:
3.3.3 Return Type
Resource methods MAY return void, Response, GenericEntity, or another Java type, these return types are mapped to a response entity body as follows:
void
Results in an empty entity body with a 204 status code.Response
Results in an entity body mapped from the entity property of the Response with the status code specified by the status property of the Response. A null return value results in a 204 status code. If the status property of the Response is not set: a 200 status code is used for a non-null entity property and a 204 status code is used if the entity property is null.GenericEntity
Results in an entity body mapped from the Entity property of the GenericEntity. If the return value is not null a 200 status code is used, a null return value results in a 204 status code.Other
Results in an entity body mapped from the class of the returned instance. If the return value is not null a 200 status code is used, a null return value results in a 204 status code.Methods that need to provide additional metadata with a response should return an instance of Response, the ResponseBuilder class provides a convenient way to create a Response instance using a builder pattern.
‘Regular’ beans are mapped over in pretty much the same way as Response is, with the exception that a Response allows you to set additional metadata (response headers, specialized status, specialized content type, etc). As far as which one to use, thats entirely up to you too decide – Response gives you more flexibility, but regular beans are more ‘self-documenting’.