My main use for a hiking app is to keep track of things like my pace to maintain the proper rhythm (not too fast or slow), elevation profile, and all those sorts of other metrics. I don't count on it for mapping, though the app I use does have some basic mapping capability.
The app I use is Walkmeter. I really like it and it has tons of use for tracking and logging training hikes as you work up to big goals like Whitney. I know everything from how many feet I've climbed on trails this year to how many miles I have on my hiking boots.
I'm sure there are folks with a lot more experience with different apps, but that's my 2 cents.
