We recommend using basic types to build up your request objects — that means strings, integers, booleans, and so on. We're just abstracting away input parameters. You should be able to consume Application Services independently from the delivery mechanism. Even pretty complicated HTML forms get translated into basic types all the time at the controller level. You don't want to mix up your framework and your business logic.

With certain scenarios, it's tempting to use Value Objects directly. Don't do it. Updates on the Value Object definition will affect all clients, and you'll be coupling clients with your Domain logic.