A concrete recommendation (but only 2 datapoints):
I had a Kingston NV2 2TB at first in my mixed NAS (mostly HDD and some SSD for more latency sensitive data), now a lexar nm790
The Kingston would suffer from read speed degradation and use more power (no ASPM and lower power states supported), and have pretty bad write consistency when transferring more than about 10 GB.
The lexar drive doesn’t have read speed degradation (at least for the over 12 months of use) and better write consistency and lower power use.
Both are very cheap per TB (though successor models are available for both, though the nv2 is not available any more but the nm790 is). The lexar drive is TLC, the Kingston might be tlc or qlc via lottery. Both are dramless but haven’t noticed issues particularly especially with the Lexar.
If you are planning bigger writes avoid qlc or potentially qlc drives. They can get very slow for big writes (like a lager backup?) so that they might not even saturate 2.5gb. It’s also more likely they develop read degradation.
Maybe take a look at the read degradation thread on the forum for info. It could be a concern if you use ssds for long term cold storage as one might on a nas.
Personally I run monthly btrfs scrubs to check for bit rot. Basically sequentially reading all data. The NV2 would would drop below 1GB/s after a while (I think it was 6-9 months), so I’d run a btrfs balance periodically (rewriting the whole filesystem) to mediate. The lm790 still scrubs at 4-5 GB/s after more than a year. As does the Kingston KC3000 on my desktop.
But basically get a cheap TLC drive, with no read degradation if you can find data on this, and you’re good to go. Pcie 3 or 4 shouldn’t matter.