My question would be why you are going to old/2nd hand gear?

It may be becoz you can get it quickly, but the performance sux compared to new gear.

Most of your list is around the 10TH / 1kW range which is the same as miners many years ago.
Even an S9 falls in that arena (and better than that) and some people think S9s don't exist any more or are not worth running any more.

Current miners are around 90-100TH / 3300W so up to 3 times better in H/Joule

Diff is on the rise again and may well catch up to the previous peak in the not too distant future.
Consider that also when considering buying now, old slow poor performance miners.

The high failure rate isn't something confirmed by any scale, these gears are just a rebrand of other miners (mostly INNO), so their failure rate is within the range of the original piece of gear, but that's great advice nonetheless, those gears shouldn't be bought.

OP, it seems like you have free power and you are looking for the cheapest gear possible, I know this is outside of the scope of your question but do you know what it takes to run a single unit that consumes 6000w? do you have any background about electricity, wiring, MCBs, fuses, amps, volt, and all that?

The reason why I ask is that where I live power is either free or almost free, so most newcomers take your route, I was contacted by so many folks who bought BITFURY gears and most of them had troubles with electricity, this beast sucks a ton of power, despite the fact that it takes 2*C19 power cords to run it - the infrastructure needed to run such gears isn't available at home, so most people end up selling it for a lot cheaper to those who have the infrastructure needed.

With that being said, according to one person who I trust and know he has been mining for years, he said those gears are very robust, but the power consumption is out of the question even if you had free power, it will be limited/capped by something outside of your control and thus you won't be able to expand, so I'll add my vote to NFW and say go with Avalon.

You better have free power and it better be a VERY inexpensive price for the miner... That is horrible efficiency even compared to the Avalon 921. Beyond that, there has been very little mention of Bitfury gear here, mainly because most of their production of miners is for use in their own farms with very few sold to outsiders (consumers).

Which Avalon miner? There are several different ones but at 20TH I'm guessing the A921? While it is a solid miner (all of Canaan's miners are very well built) it is not very efficient, power used is more like 2.0-2.2kW depending on air temperature. I would go with any of their A10xx, A11xx or A12xx series. I must add that while all of Canaan's miners are fairly easily serviceable and have good built-in diagnostics, getting replacement modules for non-current miners is rather hard to do as Canaan did not make make very many of the modules for use as spares.

Forget about Ebit, Axin, Aladdin and the Lovecore A1. They all have high failure rates along with terrible to non-existent support.

Alladin, Aixin, and a1 miner don't have official support and I'm sure it will only give you a headache.

If you want a better ASIC miner then go for Avalon I only heard few people experienced some issues about this miner compared to other miners you mention above.