I can only speak for the Apex, although the GHL seems like a great one as well.
I just got the new Apex recently and have been really enjoying it. It does exactly everything that I need from it, monitors and keeps me abreast of anything wrong in the tank.
The thing these days is people are carried on with controllers to ridiculous aspects. IMO the point of that equipment is to monitor and inform us of events such as temperature swings, power outages, and in my case, shut the return if water gets all over the floors so my wife doesnt kill me.
GHL is a robust controller, with easy set up and excellent quality. The Apex has awesome support, is ahead on whats trending in the hobby and IMO has cool looking equipment.
Neptune's reliability took a hit when the new unit came out due to component issues, but those have been repaired and the company was always straight forward during the repair times. I was one that bought it and returned a few months back.
One can go on and on about controllers, the tech geeks, but technically with either one you should be happy.