I own GPSNavX, MacENC, and PolarNavy. Of the first two, go with MacENC, it is a superset of GPSNavX and will read several extra useful chart types. I used that for many years, but now use PolarNavy mostly. It is not as fully featured but has most of what you want, and has the big advantage that it stitches raster charts together. MacENC does not. For most use, I like the charts stitched, then I can see where I've been, where I'm going, etc. With MacENC as you pan, it automatically opens the next chart, but does not stitch the border. Every once in a while, that is good, because you can see exactly what is on exactly that chart and in fact you can tell it what chart you want to be looking at. PolarNavy guesses what chart based on position and zoom level, usually pretty good but sometimes not. Also the stitching process can obscure one part of a chart - sometimes exactly the part you want to see, like are the soundings in feet or fathoms? (MacENC always tells you...).

For support, you absolutely cannot beat MacENC. I don't know the guy, but he must sit at that computer 24/7. I have been late at night on both coasts, emailed a question and invariably I will get a response within hours, usually minutes. It will be very brief, but knowledgeable. PolarNavy on the other hand, you may get a response in a few days, or maybe not ever. But both programs work pretty good and are relatively bug free.