As a seasoned Spring user I was assuming that Spring Integration would make the most sense in a recent project requiring some (JMS) messaging capabilities (more details). Af
I only recommend Spring Integration if you already have got a Spring project and you have just to add some "basic" integration using File, FTP, JMS, JDBC, and so on.
Apache Camel has two main advantages:
Because Apache Camel has very good integration with Spring, I would even use it instead of Spring Integration in most Spring projects.
If you need more details, you can read my experiences in my blog post: Spoilt for Choice: Which Integration Framework to use – Spring Integration, Mule ESB or Apache Camel?