Really depends on how much you want to spend, and how you want it set up.
I have an autocom, and it is great. We have the satnav and phone linked in to it too. The power feed for mine is taken from the read light feed (a common arrangement), and the box itself sits on top of the abs pump, which on your bike would be the storage area under the seat and just behind the rear damper. i have the two cables come out between the seat and tank. When I'm riding on my own I can lift the seat off and tuck them under there easily.
As for switching it off, it is fed by the lights as I said so if I get fed up with the screams i just turn the lights off and hey presto - it all goes quiet(er)
If you really want to have a switch then buy a PTT (push to talk) switch. Then only speach comes through when you want it, and not automatically based on speach volume.
Getting the speakers and mic in the right place is quite possibly the most important part of the setup. If the speakers are off by as little as 15mm it drastically cuts the volume down. If the mic is not positioned correctly then it will pick up wind noise at speed. I would think this must be true of all systems. Take some time over fiting them to the helmets. Possibly even link an mp3 player into the autocom and experiment with the speaker positions with the helmet at home, before you even go out on the bike. It will save you a lot of playing about later.
The bluetooth wireless systems seem quite good, and from what I understand fairly easy to fit to / remove from the crash helmets. They have the advantage of not needing to wire into the bike, but do need to be regularly charged. No idea how they last when used for satnav directions, as obviously battery life is dependant on how often they transfer data.
Hope that helps.