I used leaflet for a previous project involving maps of users (https://tagmap.io/tag/slatestarcodex is an example of one), and my experience with it was wonderful; I'd be happy to use it again next time the need arises. The best part about it for me was perhaps how easily configurable it is, including easily adding additional plugins (for example, we used one called MarkerCluster to cluster markers for users if there were hundreds or thousands in the same area. Changing the style of markers, adding new ones, and so on, was also trivial). Nice library and experience in general.