I might be wrong, but I thought the advantage of the antenna is that the unit can pick up a signal pretty much regardless of the way you are holding it; I thought the antenna was effectively four different facing antennas arranged in a square, where as the more 'ergonomic' devices have one flat antenna integrated above or below the display.
I can't comment on whether the 60C(s)x units are the best, but they are very good and I'm very happy with mine. I've had several types of GPS units over the years, and the both the 60CSx and 60Cx are the quickest to aquire, most solid to retain and robust to use.
The caching software is basic on the unit - essentially you can classify one type of waypoint as a 'Geocache' and then the unit will allow you to 'find' and 'locate next nearest' etc. It's not great and on it's own does not provide enough information to go paperless.
I used GSAK to manage my Geocaches on the PC, and take advatage of it's ability to re-map the geocaches to a set of custom icons on the GPS unit so you can see if caches are traditional, multi etc. This makes the unit more useful, but I still take a PDA with GPX sonar on for more information.