The very idea that someone owns mapping data seems weird to me. It's the real world, people can just go and see what's there, how can someone claim to own location info?
It's possible to find value from both for different reasons, realise they excel in different ways, and my contributions to each reflect my use of each.
Into Google I add/update business opening hours, locations, photos of the inside of a shop or space, reviews of the produce or service on sale (with more positive reviews than negative). These are the things I find of most value when I travel to another area or country.
Into OSM I add/update paths, geographic features, detail on the ground. Things that aid navigation, location, a more factual rather than subjective view of the world around. These are the things I find most of value when I am travelling or researching history and wanting more factual information at a fine level of detail about a collection of places (an area).
I find no contradiction between contributing and using both, because my reason for using OSM and Google services does not boil down to ownership of data.
That said, there is an area in which I actively promote OSM... cycle navigation.
The Garmin maps are exorbitantly priced and always out of date. I promote (on over 300 cycling forums that I run) the use of Open Cycle Map, the ability to load these for free onto a Garmin, and the quality of them across most of the world.
But then... you didn't mention Garmin ;)
One only needs to consider "whats in it for me". Whats in it for them is that their edits show up on Google Maps. They use Google Maps, and so the service and product they use improves.
The OSM "whats in it for me" is identical for the normal user. If normal users see that their app uses OSM then they would be more likely to edit it. This is why OSM requires attribution. It of course has additional benefits - edits are not moderated, anything can be edited, anywhere can be edited, you can get the data, if you have your own site you can make your own maps. For many normal users in both Google Maps and OSM they don't think about the Freedom aspect of their contributions (I'd imagine more would with OSM).
More worrying - we have seen VC backed companies in the OSM ecosystem quite loudly state that the Freedom of the data is less important than getting people to use it, because they see people contributing to Google Maps and because in their minds non techies don't bother about Freedom.
1. I use and benefit from the resulting services Google provides.
2. There are plenty of good personal and commercial reasons to want accurate data in Google Maps.
I sympathize with the feeling, but if one likes and uses Google Maps, contributing benefits you and others like you, not just Google. Avoiding it because you're not paid is a bit like cutting off the nose to spite the face.