I can't speak in depth on Foreflight or WingX, but I do use the Garmin Pilot app on my iPad mini with the Garmin GDL39 GPS receiver. When your subscription ends, you are no longer able to log in to the app.

Foreflight and Garmin Pilot allow you to install the app and try them, fully functional, for 30 days. Both apps are pretty similar, and both had features that I really liked. In the end I settled on Garmin Pilot because it allows you to customize the moving map as either a sectional or the GPS style similar to what you are used to seeing in your car based GPS units. Foreflight is sectional only. Garmin also offers a feature that overlays airport diagrams right on the moving map, complete with runway and taxiway designators, and will automatically zoom in as you near the airport.

Both Garmin and Foreflight use proprietary GPS receivers (GDL 39 or GLO for Garmin and Stratus for Foreflight), but will also operate on wifi or cellular data.

The nice thing about the iPad/iPhone apps is that they are constantly being updated and will notify you when updates are released or navigational data is out of date. Both have very intuitive interfaces.