I went for the
Cardo Scala Rider Q3 Multi-Set. The chief reason I went for this one was because I can plug my custom SoundEars straight into the unit without having to modify it.
I got the Multi-Set because it wasn't much more expensive than a single unit at the time of purchase and then I could have one in use and one charging whilst riding. Or if I'm riding with a buddy in a group they could use the spare.
I like that it can connect to 2x bluetooth devices and and up to 4x intercom links (I've only ever connected to 1 other unit but have connected it to the Zumo 660 and my Iphone4). You can also connect an mp3 player up to it with a cable (never used it as I listen to audio via the Iphone or the Zumo).
It's good for up to about 1km but you might get more depending on terrain. I like that it has FM radio, which I use a fair bit and the Click-to-Link feature that allows you to connect with other units on the fly without prior pairing (although I've never used this feature).
It's firmware is upgradable and you can adjust various settings using the software like FM presets, VOX sensitivity, hot dial etc... another good thing is that they are compatible with a bunch of older Cardo units which have been very popular.
The speakers are loud, clear and crisp even with ear plugs and the same for the microphone. I really like the sleek design and the build quality so I would fully recommend it.
The only caution I'd say is to make sure that it's properly connected to the cradle with a firm 'click' before you ride away.