I don't feel there is a "best". Comes down to personal preference on the features and functionality you are looking for. Lots of great options. And, I am an owner of one of the companies mentioned.
Only have experience with the kuiu harnesses. The new pro has worked awesome. You can detach binos from harness completely without taking the harness off for glassing
AGC user here as well. I use it to carry an extra mag, pocket drag, flashlight, scanner, and extra batteries for everything. Haven't tried any other chest packs so can't compare to other brands, however, the AGC works perfect for my use and I've had no need to try something else.
I own 3 different brands and they are all I’ve ever tried and I tend to modify a lot of my gear rather than switching between a bunch of brands. I just can’t help it.
I don’t know if there’s a perfect harness but I know I want 3 main things
1) simple low profile design, I don’t want a bunch of pockets.
2)be able to easily unclip the binos from the harness.
3)forward opening with minimal noise.
-I use a large BinoBro Pro for my Leica Geovids.
It is simple and works great for me. But it’s not in original form.. With this one I added a thin, stiff plastic liner inside. It was easy to do and didn’t take long. I did it because the split bridge of the geovid was hanging up a little on the clothe material when taking them out. Now it’s smooth. I also added some quick disconnect straps to the shoulder straps of the harness. Also an easy mod.
-I Have a Muley Freak for an 8.5x43 MinoxHG. It works great. My brother has the same binos and wanted to try a harness so I lent it to him for one of our sheep hunts a few years ago and it never came back to me.
-Then I bought a used older model Kuiu for my Minox binos. I wound up permanently attaching the pouch to the harness shoulder straps and adding quick detach straps so that it operates like most others designs. It works great to but definitely not in its original form anymore.