Debian is put together by a community of volunteers rather than having the backing of any commercial organisation. This means that new versions of Debian are released when the community regards them as ready for public use rather than when shareholders expect a release. The benefit of this approach is that stable releases of Debian tend to be very solid.
...
In summary, if you have no specific need for an RPM based solution - use Debian - the software is solid, they have a good security track-record and management of the system is easy once you learn how to use the tools. If you have a need for an RPM solution or plan on working with Red Hat at some stage in the future, use CentOS.