I live outside the US and struggle with a good mapping solution... I make a point to stick with Apple Maps on my phone but sometimes I am forced to resort to Google Maps to find some place I know exists but Apple Maps doesn't have it :/
So I just tried Mapquest and it had the same problem :(
Google's mapping dominance outside the US is really only challenged by Bing maps... which I can't get on iOS. Nearest is HERE maps but it's not quite the same product.
I've used Here WeGo in several European countries and it didn't fail me yet. I would use OpenStreetMaps but I couldn't find any OSM app with public transport included as an option.