I've been using Back Country Navigator Pro for a while now, and I've been fairly happy with it, but recently I came across
Locus Map for $12 on the app store. It has quite an internal map marketplace with numerous available online, offline, and trail map resources to purchase. It came with three free "LoMaps" for offline state maps, I picked Kansas, Oklahoma, and Missouri.
So far I'm very impressed with the app, it has a very good UI (much better than Back Country Navigator), built in geocaching things for people interested in that, and when I imported my KMZ files from Google Earth it even pulled in the line colors and Icons that I'd made!
The topo map data isn't quite as good as the ThunderForest maps that BCN uses, but everything else is much better.
I haven't tried it out yet but there's also a (subscription based) live tracking function for sharing location data with friends & family similar to services that Spot and InReach offer, but dependent on mobile data for functionality.
If you're using an android device as a GPS, maybe check out the free version. I liked it enough to spend the $12
(I'm not affiliated and don't receive anything for a referral - just sharing a sweet app I found with the group)