Some very interesting star clusters in your images, John.
The most massive and compact Milky Way star cluster that springs to mind is the NGC 3603 cluster (I think that the cluster and the surrounding neb probably have the same NGC number)
This cluster is neither exactly an open star cluster nor a globular cluster.......it is so massive that it has adopted the structure and symmetry of a globular star cluster, so it is best thought of as a newly formed low mass globular star cluster (that is, with young stars).
Nonetheless, a tough object because of its small angular size.
Another of these clusters straddling the Open-cluster/Globular Cluster boundary is Westerlund 1 . However, I am not sure if recent research still supports this conclusion.
Taking an overview of the cluster population in our own Galaxy and elsewhere in the nearest galaxy groups, it would seem that the most parsimonious interpretation of the highest mass
young clusters known in the nearby galaxies is that these are newly formed
young globular clusters.
cheers,
bad galaxy man