[cflat]

5.25" floppy disks are more likely to suffer physical damage at this point in history than a 3.5" disk. This would also contribute to the supply-demand curve biasing to 3.5" (on top of the ubiquity argument)

3.5" have a more durable design - the hard plastic, the spring loaded shield and, most importantly, the center disk that rested on the enclosure housing that prevented the magnetic medium from sagging.

When 5.25" disks are stored on end, they sag over time causing them to physically be unreadable. You have to store them flat. 3.5" are (mostly) resistant to this sag and therefore will be more likely to survive long term.

[jfengel]

That's what I was wondering: if you came upon a cache of 5-1/4" floppies, what are the odds of them being readable? How well will the magnetic media hold over, say, three decades?

(While I'm sure there are lots of reasons you might want a floppy drive, the case I have in mind is "Hey, here are our old financial records from the 80s" or "I wonder what's on this disk in grandma's attic".)

[souprock]

3.5" disks are less durable. The sliding door snags inside the drive. This destroys both the disk and the drive.

[Doxin]

I can see the slider getting snagged, but I don't see how that can destroy the drive. At least for the model drive I have the slider clears way before the floppy gets near the head. Worst I can see happening is the floppy getting jammed inside, but that should be easy enough to fix given a screwdriver.