Hi Anh and Michele,
I think the main issue here is that Google could change their Terms of Service again and reduce the “free” offering, whereas OpenStreetMap is open source meaning that if Metabox incorporates OSM there should never be an issue.
In addition, OpenStreetMap uses data collated from a wide variety of official sources (including Geonames) so it’s very reliable and the open source nature of the project means it fits well with the WordPress way of thinking.
There are many mature GPL plugins on the WordPress repository that facilitate OSM. Presumably one of these would give a good starting point for integration: https://en-gb.wordpress.org/plugins/tags/openstreetmap/
OpenStreetMap gets my vote.