I like that it is easy to connect leaflet to web page. It allows to use third party map tiles like mapbox tiles. It allows to customize map, add some additional settings for final user, like markers with popups where each popup can exist any text and even fields which user can edit. Markers can be grouped to clusters and when final user zoom in a map, clusters are divided to smaller clusters and finally to separate markers. It is possible to customize markers, make their look unique. Use different third party extensions and so on. I think it is the best JS library for working with maps. It uses openstreetmaps, so it does not cost anything for developers.

Easy to use, lots of tutorials, large helping community.

If it is your first time to create an application that requires maps, Leaflet is one of the best to use for beginners. Leaflet has a nice and easy to understand documentation. Since it is a well-known library, you can see a lot of projects and video tutorials online which you can use as your reference. Another reason for recommending Leaflet is because of React Leaflet, which makes map creation and customization a lot easier.