[GPSNavX]

The charts are the same data, but there are some key differences in the apps and regions available.

iNavX offers ..

Access the largest library of up to date official charts and maps
Comprehensive route and waypoint management and navigation including auto-next
Import/Export of waypoints, routes and tracks in both KML and GPX format
GRIB Weather overlay (wind, pressure, waves, precipitation rate and temperature)
Anchor alarm
True and Magnetic bearings
Great circle computation for all bearings and distance
NMEA-0183 and N2K display and waypoint import/export via TCP/IP
AIS target display
Digital compass
Instrument display
Chart and route printing
Chart emailing and tweeting
Course Up chart orientation
Full screen display
Runs on both iPad and iPhone (Only need to buy once)

The big difference is with Navionics charts from X-Traverse you get the very latest versions (and all updates) of the charts and you get access to regions not available on the Navionics apps. Super regions 1 and 3 and the Fish'N'Chips bathymetric charts.