GaN amps are not unlike other amps and each manufacturer has a slightly different interpretation and the resulting sound can be quite different. I have a customer who just did an Atmasphere vs. AGD test. Both amps are great. He liked the AGD better because it sounded more like a stereotypical MOSFET design which is quite tubey sounding. His system needed a more musical amp and he looking to move away from Leben. If his system was more musical, the opposite result might have been the case and the drier Atmasphere amp could be a better fit.
I personally have tested Peachtree vs AGD and again, the Peachtree is brighter and more sterile. It doesn't make it bad, just different and needed to be paired with different speakers.
There is never an objective "best" amp. It is what is best for your taste in your system.