Google Maps, Apple Maps, Organic Maps and OSMAnd+. Although Im very willing to admit that "best" is highly dependent on my rather specific personal preferences. Being FOSS gives OSMAnd+ a big plus (hehe), but I also have an interest in GIS, which it is quite good in, since its a rather information dense app. From the sometimes absurd categories that you can search for (e.g. "abandoned", which is great to search for Urbex targets). I also love the bonkers level of personalization you can achieve with OSMAnd+, considering that the alternatives have very little options on mobile phones.