Depends on what you are looking for and what country you are in. When it comes to small 'unofficial' roads, bike paths and hiking trails then OSM is much better. When it comes to finding the location of rural buildings, addresses and companies I find Google Maps much much better and complete, at least here in Sweden.

Yes. On the more critical part when in the middle of nowhere I often use a traditional map as reference after getting my rough position through Google Maps. I wouldn't trust any of the mapping services more than the local entities to provide accurate trail info, especially as they're the own maintaining the paths.

Sadly I'm still not good with really basic compass and map positionning, and the GPS + average location info helped a ton in the past.