Google Map Maker
Google Map Maker is Google's system for "crowdsourcing" geodata. It is a direct rival to OpenStreetMap in terms of competing for contributors and map editing contributions. OpenStreetMap is better than Google Map Maker for one simple and very fundamental reason:
Google Map Maker is a closed system.
Only Google gets to choose what can be done with the data you enter.
You input geodata, the positions of roads etc, you see it on Google Maps and in a range of services and tools produced with the data, but...
You can't get your geodata back out again. Google owns the underlying data and they protect their commercial interests by keeping this locked away (even though it was contributed by you).
If you spend time contributing to Google Map Maker, you are helping a commercial company to build their market dominance.
Google Maps possibly intentionally provides a inferior free routing service in order to encourage you to buy Maps premium.
OpenStreetMap offers open data.
Anyone is allowed to use your data - for useful, fun and exciting purposes.
You input geodata, you see it on openstreetmap.org and use it in a range of services and tools, and...
The data is available to download with an open license giving everyone the freedom to reuse, redistribute and build applications with it. The licence allows commercial use but OpenStreetMap itself is a not-for-profit "good cause" open data organization.
If you spend time contributing to OpenStreetMap you are helping a good cause, and building a geographic database of the world which is free and open for all – forever.
OpenStreetMap data can be used to provide a superior routing service. And it is. 
The difference is night and day, and yet many people fail to notice issues around the openness of their data. There is tendency instead to focus on the rendered view of the map, and other "downstream services". While we do have comparable downstream services (see Comparision Google services - OSM) OpenStreetMap is open in a much more fundamental level, and this is surely worth considering for anyone dedicating a lot of time towards contributing.
Leading the Pack
Licensing and ownership aside, many comparisons have been drawn between OSM and Google Map Maker. Both projects are attempting to crowdsource geodata from scratch and particularly so in areas of the world hitherto undermapped or even unmapped.
At the time of Map Maker's launch OpenStreetMap was comparatively more developed and detailed virtually everywhere in the world with the exception of the United States.
Citing license concerns Google decided not to use OpenStreetMap data and instead launched Map Maker as a rival. We believe that this is a mistake. Projects like OpenStreetMap that have a share-alike policy and open access to the data create a virtuous cycle.
Unlike OpenStreetMap, Map Maker is not licensed to provide access to the data. Google claims ownership of the aggregated dataset and user contributions may not be shared or used by anyone other than Google themselves.
Data from Google Map Maker is therefore incompatible with OpenStreetMap, and OSM users should not copy data from Map Maker to OSM nor should OpenStreetMap data be entered into Google Map Maker.
Initially Google launched Map Maker in a few developing countries and nations for which the large, commercial geodata companies do not have data. They treated India and Pakistan as a large testbed. They also pushed, and continue to push Google Map Maker to humanitarian aid organisations in areas where HOT – the Humanitarian OSM Team – are trying to persuade people to do it the OpenStreetMap way.
We would encourage users who are considering contributing to Google Map Maker to contribute their data and knowledge to OpenStreetMap instead. OpenStreetMap is more detailed, growing more quickly and, most importantly, liberally licensed specifically to allow new and creative uses. By making contributions to OpenStreetMap everyone benefits whereas contributions to Google Map Maker have only limited benefits at best.