Open Maps is great. I'm using Organic Maps on Android. Download the relevant maps for your needs, then you don't even need internet connection. Why FOSS devolpers use Google Maps? Probably the usual disease: convenience.
Discussion
oh yes. I use OSM and +
Don't know the exact differences to Organic Maps.
Yeah, I cannot start the project with 100% functionality without GOOGLE MAPS API KEY, and that sucks.