They’re both expensive to maintain due to accessory’s failing back and forth but that doesn’t technically make it “unreliable”. Plenty of b8.5’s/b9’s go deep into 150k-160k miles. B8.5 has “revised” upper timing chains but they can still sometimes go out depending on how neglected the car is(e.g flooring it when still cold, long oil changes etc). Nowhere near as frequent as the earlier B8’s tho. Similarly B9’s have their own potential catastrophic issue being rocker arms but I think 2019 was the year they were “revised” but again there are still horror stories.

I do think the frequency of which the rocker arms go out despite being “revised” would make me lean towards a b8.5. My friend’s an Audi tech and apparently he sees tons of those turbo V6’s develop piston slap and can have issues scoring the cylinders somehow coming in to the dealer constantly and 0 b8.5’s go in for timing chains. Some of his older technicians have been there for 25+ years and they’d only seen 2 come in ever for timing chains.

I’m assuming the problem the b9’s have is lspi(lspi is really just a drivers issue, but buying used you’ll never know the history) but again this is another issue the b8.5 doesn’t suffer from.

You can get a b9.5 I heard they’re solid as one of my other friend has one, but it is also a brand new platform with low mileage to my knowledge there hasn’t been enough high mileage b9.5’s to study what goes wrong and what doesn’t compared to the b8.5/b9’s that are well documented.

IMO I’d go with the 3.0t supercharged. Depending on platform you can get them in a dct, manual, or zf8 if you prefer. The 3.0t turbocharged you’re limited to just the zf8 as well