According to the wiki on chat commands and this image, /team will send a message to your team in WvW and /map sends to all players in your zone. Does the /map allow everyone, including enemies, to see your message?
This has actually been answered by Jon Peters (if I recall correctly, but it may have been another developer) in the now defunct official GW2 forums during beta weekend #3.
In his words, in WvW /map and /team channel are currently implemented to be absolutely identical. This of course means that enemy worlds can not read the channel. (He also elaborated on how ANet had planned to disable one of the channels in WvW for the sake of clarity, but this turned out to be more complicated than initially thought, so they left them both in the build.)
Unfortunately, I cannot give a link to post since the official forum has been wiped again after the end of the beta weekend. Also note that this is information regarding a beta build, and things may change before launch.
Looking at this quote on the wiki
All players in your current Zone or City
I would interpret this as being all players on the map regardless of which world they are playing for. So I would assume that using
/m is public.
I'm not sure what the range of
/s is either. Probably best just stick with
/p (party chat)