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). After some days working with Spring Integration it still feels like a lot of configuration overhead given the amount of channels you have to configure to bring some request-response (listening on different JMS queues) communications in place.
Therefore I was looking for some background information how Camel is different from Spring Integration, but it seems like information out there are pretty spare, I found:
We choose Camel over Spring-Integration because the fluent API is really nice. We actually use it in Spring projects and use Spring to configure part of it. The programming API's are clear and there is a large set of sensible components.
We did a small scale shootout and basically at that time for our requirement Camel won. We use it mainly to transfer internal datafiles to/from external parties which usually requires format conversions sending it using ftp/sftp/... or attaching it to an email and sending it out.
We found the edit-compile-debug cycle reduced. Using groovy to experiment setting up routes are added bonuses.
Spring-Integration is a great product too, and I am quite sure it would satisfy our needs too.