OK hotshot, how sure are you that the medium those *wonderful* answers are stored on hasn't deteriorated, resulting in us looking back on bad advice?!
Assume it will, or that it already has. Which, has more or less been in all those answers which came before.
Buy 4 HDs ... back everything to all four, keep two at home, and keep backing up to them, put the other two in another physical location. Periodically rotate one of them.
If you have at least two backups of very recent vintage, and two of an slightly older vintage ... you're constantly making new backups.
Over time, assume even the ones you're still using.
In other words: Hint: The consensus recommendation was to pick at least two different media, and store them in a least two different geographical locations, then migrate to different media as technology improves.
Which is precisely what the GP said.
Don't assume you've made a static backup which will suffer from neither bitrot nor obsolescence. Plan accordingly.
This is literally a decades old strategy. The more important the data, the more discrete copies you keep, and the more regularly you do it.
What makes this Ask Slashdot different (it doesn't, but here goes) is that the submitter is asking for the best long term media for a personal archive, which implies storage untouched, for long periods. In other words, if I die tomorrow, how can I be sure my great grandkids will get to see my vacation photos in 2077 after my worthless kids and their worthless kids shove all my shit in their basement to deal with "next spring"?
It seems to me that the correct question is either: A) what backup service can you pour money into today with the hopes that it will outlive you and keep your data safe? or B) how do I convince my worthless kids to rotate my archives off of SATA3 disks in 10 years when the last compatible PCs are getting recycled?