So now we've established that fans and fans alone determines noise level in both pure air coolers and closed loop systems. We know that cooling performance is good, with multiple tests (I can link about 10 reviews proving this) that the closed loop systems can match the best air coolers.
So now we're left with the fan issue. We can go back and forth on this - There are some websites showing the 920 to be quieter than nearly every top air cooler. Such as this:
http://www.hardwaresecrets.com/article/Antec-Kuhler-H2O-920-CPU-Cooler-Review/1314/6
This test shows the antec 920 at 41db load, while the noctua 14 is 49db load. The common theme here is that different review sites are getting varying results depending on which fan the manufacturer pairs with their product. Furthermore, the noctua is 53C at full load, while the antec is 49C.
Antec has used multiple fans in their design. Their most recent is quiet. But again, the fan you use and that alone is what determines your noise level. Having used a noctua, multiple corsairs and antecs , so far the antec 920 has been the quietest with the fan provided. Its all personal preference. If you like air coolers, thats fine. I personally like having the additional space, and its not just the RAM -- just, everything is way easier with the closed loop system, from removing/replacing the CPU (the asetec system has a very easy mechanism to remove the pump), changing the upper most pci-e slot card, I could go on. I've used air coolers that are so massive that they block stuff like RAM slots and the retention mechanism for the upper most PCI-e slot...not being able to easily remove a PCI-E vidcard because of an air cooler is annoying indeed.
Anyway, to get to the point, you can't make a broad generalization that closed loop systems are sub-par. I won't go on a google spree to bore you with results , but i've seen many, many reviews showing the top closed loop systems matching and beating the best air coolers. The noise issue depends entirely on what fan is bundled. The pump is silent.
In the end its all personal preference. I like having a system easily accessible for upgrades, and the closed loop system provides me with that at a competetive price. My system is also silent, the only noise I get is from my GPU...and i'm about to deal with that via the accelero VGA cooler paired with a GTX 580.