If you look enough, you'll hear bad things about both companies... Neither Bitmain or Innosilicon is going to win any customer service awards. I've used both for years now, and in general I find their quality to be about the same, with maybe a slight edge to Innosilicon. I have some A9's right now and have found them to perform to spec and be pretty reliable, but obviously some people on the forum have had different experiences - but the challenge is always that I'm not going to come on the forum and make a post like "All my A9's work fine!", because that's expected, you're only going to post when there's a problem. I've had machines repaired by both companies - neither was good at the time, as it took a ton of time to do.
Personally I think the A9 is a better option than the Z9 - the efficiency difference means a longer effective life, and more better return.
Thank you for that answer! Exactly what I was looking for.
I've seen that the Z9 mini (especially batch 1) can overclock to great extent. I'm guessing same would go for the Z9. Have you tried to OC your A9? If so, how was the results?