I have worked in AZA-accredited facilities for most of my career, but have also worked for ZAA and unaffiliated institutions. My take is that, while not perfect and not always making decisions I 100% agree with, AZA is the best force for good in the zoo community. For one thing, it's the only *real* collaborative effort for zoo animal welfare and conservation in the US. When I worked at a ZAA institution, I felt like it meant nothing - there was no shared sense of purpose or mission, it was just a process we went through every once in a while. I don't think I could have with any certainty named five other ZAA facilities at the time if you offered me money to do.
In AZA, you have the SSPs (in their constantly changing forms), SAFE, the listservs, the committees, the accreditation process, lobbying at the state and federal and international levels on conservation and animal welfare issues - it really feels much more like a cohesive body. We're constantly working together and supporting each other to a degree I never experienced in ZAA. And the result is a constant drive to do better. When I worked at a ZAA facility, the question was always, is this good enough for USDA inspection? If so, great, it's fine. When I switched over to AZA, I ironically noticed that I became a lot more critically of the facility, even though it was better than the ZAA one - and that's because the drive there was on constant improvement, not being "good enough."
Again, there are sometimes I wish AZA would take a more restrained approach in some aspects - and others in which I wish it would be more vocal and outspoken. There are some facilities (especially smaller ones) which I feel like have lost accreditation when maybe they really just needed more support and outreach from the rest of the community. I've posted several times on here trying to correct the misapprehension that AZA is "forcing" some zoos to phase out species that we are all fond of, so I won't repeat that here. So yes, I'm overall supportive of AZA. Do I wish some things were better, yes, and I will continue to advocate for those. But right now, I still think it's the best thing we've got going as a zoo community in this country, and I'd love to see more facilities joining.