We are using Maven for a large build process (> 100 modules). We have been storing our external dependencies in source control, and using that to update a local repo.
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All politics/religion aside, licensing makes a difference for some organizations.
Nexus is GPL now AGPLv3 and now Eclipse Public License (EPL).
Artifactory is Apache licensed LGPLv3 licensed as of version 2.1 of the product.
You may also want to consider Archiva, just for comparison's sake. It's Apache 2.0 licensed.