[Aachen]

I would second CoMaps if you're just starting out. Google has some unique features like tracking everyehhh—I mean traffic data! (Tracking everyone is sometimes legitimately useful :P) and they got businesses on board by displaying Google Maps information alongside Google Search results, so all business owners seek out to add their data to Google for free whereas in OpenStreetMap (and other competitors) someone needs to painstakingly find all the businesses themselves. So business info is much less complete.

On other fronts, like hiking trails or public infrastructure, you'll find OSM much more accurate, especially around the world (I hear that Google is comparatively good on their home market). If you want things like trip planning, nautical maps, road avoidance, and tons more features: OsmAnd can do basically everything but the sheer feature count also clutters the UI. I have no problem with it but others say they prefer CoMaps and other apps for the simpler tasks, so just be aware of the different pros/cons and enjoy :)