I've used a few while cruising, Maptech Ocean Navigator, C-Map and The
Cap'n.

In my opinion, the best and easiest to use is Maptech's. Unfortunately,
you have to use their proprietary chart sets which do not have worldwide
coverage. The Cap'n can use a variety of different chart types, which
is nice, but I never could get to the point where I liked their user
interface even though I used it all the time we were in Ecuador and the
Galapagos (Maptech doesn't have charts for the area). C-map World had
worldwide coverage built in, but has really limited functionality. They
do have one of the best tide predictors though. We found in the
Tuamotas that it was usually pretty reliable for timing our passages
through the passes of the atolls.

Hope this helps.