I just downloaded "onX Hunt" a few weeks ago and it helped a lot on our public land KY trip because it puts topo lines on your aerial images. It also has a $15/year membership that gives you the ability to download maps for offline use and gives you full GIS (or plat) mapping for your chosen state. $30/year gets you every state. I don't do either membership, but I might next year because I typically knock on 30-50 doors a year.
I also use Gaia GPS for really precise GPS use when I'm hunting way out in the backwoods. It has the downloadable map for offline use feature as well and has a ton of different map layers. I use it for some of my bass fishing too because it has depth maps for a lot of lakes. It's a $20 one time fee for the app.
I use HuntStand for measuring area and distance.
And I use ScoutLook for marking scouting locations. I might combine all my HuntStand and ScoutLook uses into "onX Hunt" next year.
I have Huntstand, Scoutlook, and onX. Scoutlook was first for me, and the one I'm most comfortable with. I use it primarily for wind and weather conditions and for logging sightings, and it works adequately. OnX isn't able to show property lines in either of my property locations, so it doesn't offer much for me.
I use onX and Huntstand. I have found myself using onX more so than the Huntstand app of late. With my ground being spread over 4 counties I find the landowner information part of the app invaluable. It gives me the ability to find out who my neighbors are and talk to them about if and how they hunt. I also like the measurement tools when laying out our food plot locations. I can measure them up without having to be at the property and get seed, lime and fertilizer ordered for each location.
I use Google Earth Pro for most of what is mentioned above. It is very powerful and free.
When I am in the field I use MotionX-GPS. I think it was $2.99 when I bought it. It allows you to store your tracks (up to 300) and waypoints (up to 2500). These can be sent to your email (or anyone else's for sharing) and saved in Google Earth then removed from the app. It has 14 different map sources (I always use the default) and you can save an unlimited number for viewing offline.
I use it to see where I walked/drove, mark sign during post season scouting, mark stand locations, mark potential stand locations, etc. It's nice to come back home and upload all this data to Google Earth and see the big picture.