USAFRet :
Flash drives...aka USB sticks(?) are much more robust than external HDD's?
"Personally I prefer SD cards because..."
Can you possibly provide some documentation on this?
Because I've never heard anyone who is involved with any data retention, on a personal or corporate level, use or recommend SD cards or USB sticks for long term data retention and backups.
Something...anything?
The fact that they may live through a washing machine cycle is irrelevant.
I can think of few worse places to hold a 'backup' of critical data.
They are more physically robust. Can drop them, drive a car over them, get them wet, etc.
In a server environment where the backups are secured in a safely designed place in a systematic fashion, longevity of the media is the dominant factor. For home use however, you have to consider all possible failure modes. House catching on fire with firemen spraying water everywhere, 2 year old toddler finding the media and deciding to use it as a pacifier, dog using it as a chew toy, 5 year old using it as a hammer, etc. That's why airliners went from recording black box data on magnetic media to solid state media.
Convenience is also a factor, as a home user is much more likely to use a more convenient backup media. It's not like you're paying IT staff to lug around tapes or external drives to perform backups. I also strongly encourage people to keep their backup on flash media off-site, which usually means taking it to work and leaving it in a drawer there, bringing it home once a month for the monthly backup. That's more likely to happen with a flash drive than with an external HDD.
While information on flash media degrades more quickly than magnetic media, storage sizes (of both media and files) are increasing quickly enough to force upgrades every 5-10 years, which is around how long you should expect data written to it to last. I am not suggesting someone backup to a flash drive, then toss it into their safety deposit box expecting the data to still be there after 30 years.