My project uses Spring a lot (core, web flow, security), so I would tend to say that I should use Spring repo
You should use the repository that provides the version of the artifacts you want to use :) If you want to use OSGI compatible artifacts, use SpringSource Enterprise Bundle Repository (EBR). If you don't care about OSGI, then it doesn't matter, as long as you don't mix artifacts. That's the official recommendation from SpringSource.
Personally, I would just use Maven Central (SpringSource does publish final releases to Central).
And if you're looking for RC, milestones, or SNAPSHOTS, you can always get them from Spring's Maven Central compatible repositories:
Obtaining Spring Milestone Releases
Milestones and Release Candidates may
not be published directly to Maven
Central, and in general are published
separately from final releases.
SpringSource hosts two repositories
for obtaining Spring milestones. The
first one should be used in
conjunction with Maven Central, and
the second one in conjunction with the
EBR.
Obtaining Milestones from the Maven Central Compatible Repository
To obtain Spring milestones from the
Maven Central compatible repository,
add the following repository to your
.pom:
<repository>
<id>org.springframework.maven.milestone</id>
<name>Maven Central Compatible Spring Milestone Repository</name>
<url>http:// maven.springframework.org/milestone</url>
</repository>
...
Obtaining Nightly Spring Snapshots
Snapshots of Spring projects are
published each night, allowing users
to verify that reported issues have
been resolved before the next release.
Like Milestones, there is a separate
Maven Central compatible snapshot
repository and an EBR snapshot
repository.
Obtaining Snapshots from the Maven Central Compatible Repository
To obtain Spring nightly snapshots
from the Maven Central compatible
repository, add the following
repository to your .pom:
<repository>
<id>org.springframework.maven.snapshot</id>
<name>Maven Central Compatible Spring Snapshot Repository</name>
<url>http:// maven.springframework.org/snapshot</url>
</repository>
Reference