Scala G4 works for me. Oh look, loads of different opinions. Always the way.
But I suspect they must all be at least adequate if people are recommending them.
Mods are easier to "judge" as owners can give an opinion of before and after, things like this are harder to compare, I have never used any of the other devices listed, got the autocom 5 years ago and found it amazing for several reasons:
1. Easy pillion communication even at well into 3 figures just makes life so much easier.
2. Listenable music up to 3 figures relieves motorway and congestion boredom and the right track(s) can really enhance a ride.
I have stuck with this thing and avoided the latest blue-tooth gadgets despite the slight inconvenience of the wires for a few reasons:
a. It is always on and never goes flat
b. I have audio cables running to where I plug in the Sat-nav, MP3 and Scamera detector so it takes seconds to plug in and ride off without trying to pair stuff up.
c. It performs very well, an autobahn "test" (yes real autobahn) allowed us to be heard at around 150, OK we had to shout into the mike, at 130 you could hold a conversation with raised voices.
If I did shorter runs I may get fed up of having to spend 3 seconds plugging in the cable each time I get on / off, but for ride-outs and touring (which is what i tend to do) it has proved top value.