JBoss Seam - Spring+Hibernate vs EJB3

We are building a greenfield application and are trying to decide whether to use a Spring+Hibernate or an EJB-3 (using CMP) based architecture for our Seam applications. We are looking for the following qualities: ease of development, speed of execution, and automated testability. We have some experience writing Spring beans and Hibernate, no EJB. Our applications will be portlets running on JBoss portal for a corporate intranet, and will have low transactional volume. With these requirements, can anyone explain why we should choose one solution over the other, and/or help us in selecting one? After reviewing the Seam Reference Guide we are left with the impression that the EJB route may be easier with Seam.