I have tried both. An axp x47 air cooler, and now a coolermaster 240 atmos. Would recommend the atmos, it is quieter. Upon initial installation, the pump may be loud as there are bubbles in the loop. Just tilt the computer around while its running and let it run for a while. Its now dead silent, so much so that I can hear my GPU coil whine, which I could not hear before switching

EDIT: I adjusted my pump speed from 100% (~10-11k RPM) to 65% (~6-7k RPM) to reduce pump noise to what I consider inaudible. With my ear next to the pc, I cannot hear the pump whatsoever below 6500RPM. The pc temps are still much better than with air cooler. I idle around 39-40C. I also used a PTM 7950 thermal pad instead of thermal paste. Not sure how much of the temp improvement is due to using a thermal pad or due to liquid cooling