I have owned more than a dozen of S9 and T9 so far and never had any serious problems with them. the S9's sometimes were a little bit glitchy but once I figured their "tempers", they have been working well for me since. All of my rigs now have records of running months straight without needing any attention or maintenance.
I don't have any experience with A7 so far. Their reputation appears to be quite good but the profitability seems to come down to low end.
A word of advice for OP is to research *properly* on any of these products. People and opinions are always tend to be bias. If one only looks into a S9 service or complaint thread, all you would likely see are to be groans, however that does not justify a claim of "90% of shit". And some errors could indeed be caused by miner's negligence: static discharge etc. Well, I had burned a known-to-work S5 with a new cheapo PSU. I cried shitty S5 for days before finding this cheapo PSU fried another S3. At the end, I still yelled it was the damned PSU ruined my profit. But, indeed, was stupidity involved? Of course, but I could just never tell.
Just my two cents.
The A7s are cheaper to compensate for the lower efficiency, and they are indeed as reliable as they claim. They're also decently quiet, as I have a bud who runs one in the basement and it's essentially quiet with the TV running. As for PSUs, a good Dell server PSU is nice, quiet, and reliable as long as you also get a decent breakout board and wire the pcie wires right. They're also fairly cheap even with wires on, I bought a 1000w Dell PSU with eight PCI wires for $30 negotiating with a guy on eBay.