We have found C-Map to be the most reliable in the S Pacific.
Navionics is excellent in some places and dreadful in others (eg in Western Fiji reefs are misplaced, not even shown and shown where there are none).
We have C-Map in the Furuno Navnet, and Navionics in a B&G Vulcan7 (which was installed primarily for the fwd scan) in the cockpit. C-Map in the Furuno Navnet and OpenCPN with GE2KAP satellite charts and MaxSea TZ on the laptop at the nav station, with a wireless connection to a tablet repeater in the cockpit.
We have found the GET2KAP satellite pictures in OpenCPN to be VERY useful when trying to determine the location and dimensions of reefs...that with C-Map is a very good combination in our view....and of course the essential Mk1 eyeball!