As cell service has improved in the more remote areas I hunt, I migrated to Huntstand and OnX. Each have their strengths. To pick one I think it would be OnX.
But for a free, easy to use app on the app store its really hard to beat "US Topo Maps" Even if you drop off a side hill into a hollow without any cell signal, you can still take a screen shot of the topo, and it doesn't cost a dime.