I'm going back and forth between Navionics and Garmin Bluechart Mobile (BCM), with iNavX in third. In practice, Navionics with nav module is superior to Garmin BCM, though Garmin BCM is trivially easy to use. What I don't like about iNavX is depending on what I do, the menu buttons on the bottom disappear and I have to reselect the chart. I find this annoying.
To me, the selection boils down to the quality of the charts and how well the program responds when using. I liked both Garmin and Navionics vector charts; I didn't like Navimatics charts and lack of detail. I like iNavX's ability to display many different chart/formats and iNavx's ability to import waypoints (via email
gpx file), NMEA
wireless interface, etc.
Depending on what you are using the iPad for, a single
app may not meet your needs. I go back and forth between the above three. Each have their pros/cons.
One question, though - many of these apps cover chart regions. Is the level of detail comparable to other chart formats, e.g., Garmin BlueCharts used on PC and chartplotter, Navionics Gold, etc.? To me, the local iPad quality and level of detail is excellent with both Navionics and Garmin. Just curious!