OS Maps
I have poured over Ordnance Survey Maps (OS Maps) probably before I could read. They are the definitive maps for walking, cycling, and campervan adventures in the UK. You can find them as paper maps, waterproof maps, online maps, mobile apps, and other formats, at various scales: OS Explorer (1:25,000), OS Landranger (1:50,000), and OS Tour (1:100,000). If you have an OS Map Premium subscription, you can access routes through this site and my maps.
I use OS Maps app in the field, together with Outdooractive, with OS Map subscriptions. I will use these maps for UK National Trails.
At 1:100,000 scale
At 1:50,000 scale
At 1:25,000 scale
A big thank you to Skirrid Systems for developing the OS Map PlugIn for WordPress.
Google Maps
Google Maps is incredibly useful in the field (you can download offline maps) for finding just about anything nearby: accommodation, art, restaurants, bookshops, museums, the list is endless. You can use it for navigation, but I do not use it to navigate by foot. Road trips navigation is much much better than the most sophisticated and expensive in-car navigation system (usually based on a Garmin code and map base).
I use a variant of Google Maps, known as My Maps for cycling. Click on this link to see my North Sea Cycle Route map. These will appear in the cycle touring pages, when I configured them to support my adventure. A nice feature is that they show my photographs in a geospatial context.
Apple Maps
Essentially, Apple’s answer to Google Maps, if this is your preference and you use an iPhone.
Open Street Map
As the title suggests, Open Street Map is publically available maps, often with surprisingly good detail. I will embed and explore these maps in future, but I have used them extensively in the past for European cycling tours.
Overall, I do not find one map and one map to rule them all, but use two apps on my smartphone, and usually a combination of OS Maps and Google Maps for navigation and research. I am starting to use my own ArcGIS Experience Map often when I am on the coastline, as it has routes (with all the faults of my plotting), and points of interest that cannot be found on the other maps, and the context of geology and nature, which are some of the reasons I go outdoors in the first place.