Scuba Doobie Do:
Personally, I own Scuba Pro MK25T/S620xTI and Atomic M1/Z2s. I also had the opportunity to use Apeks TX50 second stages paired with DS4 Stages for several months. Personally, I loved how Apeks regulators breathe, which I do believe is slightly lighter and a bit smoother than either my Scubapro or Atomic regulators but the difference is quite minor. While the Apeks second stages are far larger than the second stages on my Scubapro or Atomic regulators, I could not find fault with them. They were as comfortable and did not produce any jaw fatigue. I prefer the lever type venturi adjustment of the Apeks regulator over the knob of the Scubapro second stages, which I find difficult to rotate with my dry gloves.
As to the performance of the regulators over their service interval, I couldn't tell a difference in my Atomic regulators from day 1 to year 4 (yeah went over). I have owned the Scubapros for only one year, but so far they have not given me any cause for concern.
You're overthinking this. All the high end regulators breathe very well, to the point where the human has trouble discerning a difference in performance. Let the ergonomics, ease of service and aesthetics decide (of course it has to look good).