There are a number of apps that are pretty good. The apps I have tried are onX and Gaia, and both do the job. Any app you get should be able to operate without an cell/internet connection. Every app I've looked at adds functionality when you pay for the non-free version. That said, I've always been partial to paper maps (USGS 1:24,000), a decent land navigation compass, and/or a GPS unit. I've worked in the remote field for a long time, and have preferences formed by the experience.
