Chuck,

In my interpretation the "best" stands for: the highest quality for a
given amount of money.
Assuming you are not looking for vector-maps, take a look at
http://www.sping.com/seaclear/index.htm
SeaClear offers the basic functionalities, including AIS-support and it
is freeware. It handles various type's of chart-formats and also
handles your own scan's. There is no support or active development. The
author just made his own nav prog cause he couldn't find anyting to his
liking and he donated it to the public domain.

I use it as an addition to paper charts. When see good use of it, I
scan my paper chart and use it in SeaClear cause 1) it shows the
AIS-targets and calculates CPA and TCPA (but maybe traffic isn't as
busy in your area as here at the dutch coast) and 2) it enables me to
enter waypoints and routes and follow them. There is even an
autopilot-support but I haven't used that myself. Also the simple
installation is an advantage IMO (you don't install it, just run it
from it's own subdirectory). It works fine. Never had a freeze or
anything unexpected.

Another well known program is Oziexplorer. It is more sophisticated
than SeaClear and is very affordable. Last time I looked it was usd
85.00 and upgrades are without charge. I particularly like the very
well designed anchor alarm.
The author just announced an upgrade including AIS-support.When the
AIS-version is released I will likely switch from SeaClear to
Oziexplorer.
http://www.oziexplorer.com/
You can download a demo and get an impression.
Other than SeaClear Oziexplorer is supported fi by a yahoo group with
over 6000 members:
http://tech.groups.yahoo.com/group/OziUsers-L/

Fair winds,
Len.