I”ve been trying out quite a few map plugins for WordPress and had previous experience with mapping for Drupal. Out of this background leaflet maps marker is the best solution for WordPress in my opinion. The options for many map sources and many marker options are just great.
Of course there is still room for enhancement, e.g. directly taking the location information of articles or having the possibility to attach markers to several layers. But as Robert is constantly working and improving new features should not be far away.
EDIT: I just found out that multi-layer maps are possible, but the other way round would be nice, too.