I have perhaps a slightly different take on things than most other previous posters here. You see, I'm cheap. Not a skinflint, but also not a frivolous spender. With that in mind, read on...
Firstly, I've tried both CA and Halo headsets at OSH. Both are supplied by good people who will stand behind their product. While at OSH I purchased a Halo and haven't looked back. But that's also because I have a homebrew set of CA's (thanks to a thread in this discussion forum). The homebrew headset works great and only cost about $100 since I purchased all the components used in its fabrication.
Now why to I prefer the Halos? Here are the reasons.
1) no small wires to break. The wires to the transducers on the CA's are very fine wires indeed, which means they WILL break eventually. And being fine wires they'll be miserable to try to fix. As an avionics guy I have some experience upon which to base this statement. A broken sound tube is going to be MUCH easier to fix.
2) the CA's require the use of expensive COMPLY foam tips. I have oily ears and the Comply tips just don't last very long, even though I wash them to extend their life. Since I'm cheap I prefer the less expensive tips on the Halo, and you'll find another thread here were Ironflight started making his own tips for next to nothing.
3) speaking of making your own tips, I like the idea of being able to make ear tips from earplugs of my own choosing. The Halos make this easier to accomplish, although I'm sure it would take only slightly more ingenuity to produce a similar result for the CA's.
Although I haven't tried a set of real CA's in my airplane I can say the Halo's offer poorer shielding against RF feedback than do my David Clark headsets.
Oh, one other point worthy of note. Doesn't matter which you choose, CA or QT Halo, you'll HATE them if you only buy one set. You'll hate 'em because every time your "significant other" flies with you, she'll be wearing the "in the ear" headset and you'll be back to the old melon-squeezer headset that you thought you'd relegated to passenger use! Don't ask how I know this...
Seems my last point is never my last point as I just thought of another one. Or two. In these parts the OAT's are dropping like a greased Steinway. With either QT or CA you have to roll the foam earplugs to compress them prior to insertion in the ear. This contact with your fingers warms them up. This is waaaaaay better than the brain freeze that comes from donning frozen stiff David Clarks!
And you can wear a toque on yer noggin when wearing an in-the-ear headset, and that's a major improvement in in-flight comfort in this part of the world.