I heavily researched this last year, and it was down to the G4, Sena, and BlueAnt F4...
Here's the site I used... though THIS direct comparison didn't exist when I was looking
http://www.webbikeworld.com/motorcycle-intercoms/2010-motorcycle-intercom-comparison.htm.
I originally liked the Sena's ability for earbuds, but then decided that one of my motivations for this was to get rid of wires... not just limit them to my helmet. I also wasn't completely sold on the large knob and how low the boom installed below the helmet. I also needed a flat (wired) mike (not the boom) which eliminated the Sena beck then. Sena now has a flat (wired) mike available. I recommend putting your hand inside your chin bar to see how much room you have between your mouth and helmet, this is how I decided I needed a flat mike.
The F4 takes a hit for more than 2 riders, but that was not a concern for me. I'm either riding alone, or with one other.
Both the Sena and F4 were rated very well for sound quality.
So, I ended up with the F4, and have had zero* complaints since then. I paired it with my iPhone flawlessly... took 3 tries with my old RAZR. Also paired it to a friends Zumo, first try. Sound quality is excellent. I've found I need to wear ear plugs, as the speakers seem to be calibrated assuming you're wearing plugs. Automatic sound leveling works great, tho sometimes it seems to go up and down randomly (*only on the Ducati... not on the Connie). I've made phone calls while on the freeway, and I was told the call was clear, and they didn't realize I was on a bike until I said something. The buttons are actually not to bad to find while riding, even with my winter gloves (I've only had heated grips for a couple months now). Battery life it great. The F4 easily lasts a few days. I did pick up a cigarette charger, just in case. Range is fine. Better in line of sight... but when I ride group, line of sight is no issue. I did ride beyond the range, and the sets connected again without any input by me. Bike to bike communication works great... clear and easy to use. Single button press allows comm or music.
So, in conclusion... I have nothing but props for my F4, but would probably go with the Sena if I was purchasing today.
That's my 4 cents.