Hello Jason S,
I prefer the Oceanic 4.2. I don't have experience with any Atomic product, but I do own two Oceanic regulators and other gear including a dive computer. My wife owns an Oceanic dive computer.
We have used our Oceanic gear in California in 42F water and in the tropics in water as warm as 85F. My wife has an expensive ScubaPro regulator that does breath easier than my CDX5; however, she always dives with the second stage set to "pre-dive" as she does not think it breaths hard in "pre-dive" mode.
We both owned Mares regulators previously. They both developed intermediate pressure problems and were being continually rebuilt. We junked them--we don't even use them on pony bottles.
I use the least expensive (and simplest) Oceanic regulator on my pony bottle. When I practice pony bottle ascents or pony bottle function tests (sometimes as deep as 110'), the Oceanic reg always works.
Bottom line, I like Oceanic for its value, its functionality, and parts availability.
They work for me.