Here works as well as any others, it’s free, you can download maps for the whole UK, then set the app to run offline so it doesn’t need a data connection to work. Select hifi voice for a more human-sounding voice guidance, (although some place name pronunciation is a little ‘idiosyncratic’). Automatic nighttime maps works well, and it will usually give you two or three choices of route.
I’ve got Navmii, CoPilot Live, Here, Google Maps and Apple Maps on my phone, but I’ve come to rely on Here more and more, mainly because of the route choices; I often much prefer cross-country A/B-roads to motorways, and Here gives those choices, not all of the others do, even if you dig down through the settings options to select road/speed options, which is really worth doing.
Used all the above on an iPhone 5 and 6+.