I would generally recommend using the upstream repository packages directly, since they are tested/updated with each major release, and their maintainers are proactive in reaching out to extension maintainers that need to update their extension due to upstream code changes.
* PGXN (https://pgxn.org/ - the original Postgres community extension repository, though more "old school")
* Trunk by Tembo (https://github.com/tembo-io/trunk - very similar to pgxman, but using the more liberal Postgres BSD-style license)
Additionally its important to mention that many popular extensions are already packaged as part of the Postgres YUM and Apt repositories (https://wiki.postgresql.org/wiki/Apt and https://yum.postgresql.org/).
I would generally recommend using the upstream repository packages directly, since they are tested/updated with each major release, and their maintainers are proactive in reaching out to extension maintainers that need to update their extension due to upstream code changes.