GOOGLE EARTH.
It’s so obvious it hurts when you realize it. Reads many formats natively, or just translate your files to gpx via GPSBabel and do it that way. Most GPS units will export as GPX now anyway. Then you can export as kml and share it online via Google Maps.
Intuitive editing, ease of use, it’s no contest. Too bad you can’t upload back to your GPS or it would be perfect.
Here’s some fun stuff I did last year….
For downloading, you should be able to just read your gps as an external device and drag and drop the data through your OS. Assuming you’re on Windows, there’s always a way to do it. Try the old “show hidden Files and Folders..” trick.