What's more reliable for backups and archives - flash drives or DVD/Blu-Ray?

DVD or Bluray would be the media to use. The point of archival is that the data is written once and then stored away. DVD and Bluray media are write one media (unless you buy rw media), while USB sticks are media to which you are meant to write to, then delete the data again, and then write to them again. This can cause someone to rewrite to the stick by mistake. Also, I've seen many sticks go bad, but that is mainly because they are often used and subject to user abuse and wear.

Other than that as mentioned above, a proper storage place is just as important as the media.

Thank you. I had heard that the dye (or substrate) used on DVD/Blu-Ray fades over time and can't be trusted more than a few years, but as you mentioned, maybe it's the brand/quality.

I'll go with a quality Blu-Ray. Any difference between the write-once and re-writable?

Thank you. But with backups exceeding 8.5GB (Double Layer DVD), you'd have to chain discs, correct? I'm a little leery of the multiple moving parts. If one disc goes bad, then the entire backup set is unusable, no?

Thank you, one and all. I'm going to try the double layer Blu-Ray discs. They hold 50GB per disc.