I am with Amelia,
another happy C-head user! My husband and I have been using one full time for about a year now.
The positives for me compared to NH and AH are:
Ease of emptying, literally you lift the lid and lift out the containers. Takes seconds. It seems the AH and NH must be disassembled to empty the poop bucket. In our small head this seemed like it would be awkward and unpleasant.
Ease of replacement of pee containers. They build up scale that makes it difficult to see how full it is from the outside, so regular replacement is nice.
A secondary containment unit. If you do not pay as close attention as you should to the fullness of the urine container and it overflows, it is contained within the easy to clean out box of the C-head, rather than leaking into hard to clean places on board. Sadly I have experience with the bonus of this feature...
It is easy to clean. Simple flat surfaces that only take a quick wipe.
Overall I think all units will work well if operated properly and it comes down to what compromises you are most willing to live with. We are happy with the choice we made and feel that the benefits far outweigh the extra frequency of emptying and the perhaps more home depot look of the C-head. And of course there is a cost consideration as well.
Disclaimer: I have no experience with NH or AH and have only looked at them at boat shows, online and watched some youtube videos about them.