IME, hitatchi have been the most reliable HD brand for me.
Maxtor and seagate by far the worst.

but I guess a lot of it can be just downright random.

Thanks to everyone for your replies.

Based on internet research and your replies, I have settled on a 80gb refurbished Hitachi HDD for around 15 EUR.

andrea wrote on 2020-08-18, 07:53:

Intel486dx33 wrote on 2020-08-17, 20:25:

The title of this post reads “Most reliable 2.5 hard drives”.
Not SSD’s.

But a (gutted) SSD is the only way you can fit a modern commodity (therefore cheap) storage unit plus a SATA adapter in the footprint of a regular 2.5 drive.

Or you could use an IDE to m.2 adapter.

The smaller capacity m.2 SSDs are just as cheap as the 2.5" SATA SSDs.

I had a lot of 2.5" hdd and here my top rate:

1) Areal (ideal for 286-386-486SX era laptops), reliable, silent (max 48dB when checking outside laptop), perfectly made (like many hdd's from Japan). Hard to find and too expensive on eBay (cheaper at Buyee).
2) Toshiba / Fujitsu / Hitachi and WD usually silent (less than 49dB).
3) For PII and faster machines I use only one model: Samsung 2.5" 30Gb, silent, slim, reliable ($15 each for NEW incl. shipping, but they all gone at eBay).
4) CF IDE adapters and cards are fine for ultra compact or slim laptops (Libretto, Vaio C1, PCG-505 etc).

Avoid (if you like to hear normal HDD clicking, not loud annoying noise, for laptops it is especially important):

Most IBM, Conner hdd very noisy (usually permanent more than 52dB) and not reliable.

Here good models list (yes, some IBM have acceptable exclusions):

Areal A175 175Mb
Areal A260 260Mb 48dB

WD AL2170M 162Mb

Toshiba MK2024FC 86Mb
Toshiba MK4309MAT 4Gb 48dB
Toshiba MK6014MAP 6Gb 47dB
Toshiba MK6411MAT 6Gb
Toshiba MK1214GAP 12Gb
Toshiba MK1214GAP 8.5GB
Toshiba MK2016GAP 20GB
Toshiba MK4032GAX 40Gb

Fujitsu MHE2064AT 6.4Gb
Fujitsu MHV2120AH 120Gb

IBM H2258-A3 250Mb
IBM DCXA-210000 10Gb 46dB
IBM DARA-212000 12GB

Hitachi DK23CA-20 20Gb

Bad list:

Conner CP2124 120Mb 51dB

IBM H2344-A4 344Mb
IBM DTNA-22160 2Gb 49dB
IBM DPLA-25120 5Gb
IBM DBCA-206480 6.5Gb
IBM DARA-212000 12Gb

Toshiba HDD2214 86Mb 60dB
Toshiba MK4309MAT 4.3Gb 48db knocking
Toshiba HDD2144 6Gb 50dB

Fujitsu MHF2043AT 4Gb 52dB

Many IBM not in any list because they are gone (dead, or too noisy). Usually I use they dead bodies as containers to sell and ship CPU's abroad.

Most Seagates that I have usually too large for old laptops and too small for PII-III (around 800 Mb)