I would by default rely on Fat32, unless you needed permissions and the user information/permissions intact.

If you need larger than 4Gb files, then Fat32 will be a bad match.

Although GoG splits files to 4Gb chunks so that shouldn't be a problem with GoG games.

I'd also love to make SquashFS Filesystems and burn them directly to disc, already highly compressed and ReadOnly.

A 22 year old file system with a max partition size of 2TB, max file size of 4GB, and no journaling features sounds like pretty much the worst possible candidate for a backup drive. ;)

It's also very well supported & fairly simple.

But it depends on if you're burning media, or a drive, or if you intend on making changes or the like. Lack of journalism isn't a big deal, unless the power dies while saving a file, since otherwise you're going to be reading and not writing from it.

It also has tools to fragment later so if you needed to reorder it then sure (course with flash/SSD drives that's less an issue).

don't buy from seagate, western digital and other companies that installed backdoors for the NSA into the hardware itself.

What other companies? To my knowledge, there are three hardware manufacturers that make hard drives: Seagate, WD and Toshiba. That leaves Toshiba, I guess.

The OP wants offline storage, hence the NSA would need to breach an air gap to read any data.

For reference, see this earlier conversation.

I had a Seagate die about a year ago (with all my gamesaves), and I knocked another drive off the table (secondary archive), so I've had to buy two new drives (of the OP specification, coïncidentally). I had a Buffalo brand die a few years ago, too (Japanese make, from a reputable bricks-and-mortar store, still died just after the warranty, with minimal use —vide infra).

Heat is a killer, as timppu has already noted:
I would caution any general recommendation; as the second poster, hudfreegamer, noted: All the drives are at the mercy of logistics, meaning that any single lumper* having a bad day can easily create problems that won't show up until well after they have left the scene, creating some incentive to be a dick.

My laptop is on almost constantly, but rarely used. (If I'm gaming for a dozen hours, then the drives are obviously being used; I store all my games on one drive and all the Gog downloads, as well as some other resources, on a second.)

Personally, the Western Digital I bought to replace the Seagate that failed after only a couple of months has worked well. I like WD because they park the head (after a minute of inactivity), making them slightly more resilient (in theory; the drive a sent sailing off the table was a WD (>_<) so they aren't foolproof ;), though it does mean that every access needs to wait for the drive to "wake up", as the head lifts into position and the drive spins up to access speed (a nanocentury or two). (I'm not aware if you can turn this feature off.)

Dust is another factor to remember, too. the head is only a scintilla above the platter, so a minute particle (like ash, say, from cigarette smoke) will crash into the head and cause some damage. (Don't blow smoke onto your drives.) If you have a littoral address, then salt (sea air) is also a complicating factor. (Filtering the air will extend the life of any technology in the room.)

edit: added Buffalo & prior conversation links, corrected a couple of typographical mistakes, & added the footnote.

* a lumper is what drivers call those hired to un/load a truck.