So what are the thoughts of folks who have used Nexus and moved to Harbor?

In my experience Nexus is a bit weird to administer and sometimes the Docker cleanup policies straight up don't work (junk left over in the blob stores even if you try to clean everything), but it also supports all sorts of other formats, such as repositories for Maven and NuGet. Kind of hungry in regards to resources, though.

Nexus can be flaky, but it's pretty universal as you say. Harbor is a hard sell for me, since generally in any organization you'll need non-OCI artifact storage at some point, and maintaining 2 tools is always a pain.

We run both Nexus and Harbor. I am about to dump Harbor because teams don’t use it and frankly Nexus provides the same functionality.