I am having a tough time finding an app with maps that I want. Maybe it's different for different regions, but so far each map only has half of what I want. They either have roads, half of the maps, or the other half of the maps. Aside from finding GPX files for the areas (and unless I'm already familiar I don't know if they're complete) and loading them in it just doesn't seem "plug and play".
For all the trip planning, route finding, and navigation I've done, I don't think I've ever seen a perfect solution.
The closest might be the Ordnance Survey maps in the UK, which have amazing levels of detail. Even then, just because there's a trail on the map doesn't mean there's a trail on the ground. And there are lots of trails on the ground that are not on the maps.
For places I'm not familiar with, I use a combination of official maps, published GPS tracks, which are usually something someone recorded, and satellite imagery. And then I spend a lot of time editing and merging tracks in Google Earth, Garmin MapSource, and other GPS editors and tools.
Even then, there's no substitute for good orienteering skills so you can figure out where you are and where you want to get to.
If the maps for your area aren't so good, keep searching. Maybe Magellan has some good data for your area. I took a quick look at what they have around San Diego, and they're missing a lot of trails around Corral Canyon, Anza Borrego, and a couple other key off-road spots. But that doesn't mean their data isn't good for you.