You're asking for the best way to store your images for backup. Given that, I'm going to recommend Backblaze.
It's an online solution, yeah, but it's very reliable in both backup and restoration.
- They even backup external drives connected to your computer.
- I pay about $5/month, and have had a couple of occasions where my Lightroom catalog has become corrupted, and I was able to restore a much newer copy from their backup, than from Lightroom's weekly backup.
- I've also had my entire Lightroom drive fail (bad luck, I know), and they overnighted me my data. You pay a fee for them to ship you your data vs you downloading it yourself, but you get a full refund back if you mail them back the drive within 30 days.
No fiddling with discs, no switching to Blu-Ray 2: Electric Boogaloo, if we don't all switch to flash memory and wireless by then, just backup.
Err, sorry if that sounds like an ad, I'm kinda thankful to them after saving my catalog so many times (a few catalog file corruptions + 2 drive failures).