For navigation to a known address, OSMAnd works great. Google Maps is better at search, particularly for commercial destinations, and has a slicker interface. For everything else, particularly navigation off road (on trails or otherwise) OSM excels. OSM has much more detail than Google Maps for things like parks and trails, frequently even having the locations of water fountains (this has saved my ass a few times.)

I guess my point is the alternatives to Google Maps aren't perfect but they have a lot more to offer than many people assume. When I drove across Canada, from Ottawa to Anchorage, OSM never let me down. It's a viable alternative.