I prefer optical media. HQ DVDs have never failed me, low quality DVD-DL have, but, who’d use cheap DL media for backups?
I put some disks at relatives houses in case my house goes up in flames or whatever. + the write once disks are less susceptible to trojan attacks. What use is a USB backup drive if it’s always connected and could be erased, hacked, dropped, or fail at any time. (Well, I have a Time Machine backup as well, but trust Opticals more)
High Quality BD media are difficult to find, and my burner doesn’t seem to be very consistent. It was easier in the days of 8x verbatim DVD+r. I’d have to say I had good success with Sony some years ago, but later Sonys aren’t the real deal. Neither are TDK, have had many TDK coasters. Have some garbage Riteks here as well, can be Sony or TDK, I don’t remember, I use them for DVD backups as they won’t burn reliably beyond 15 GB. Some burn great to 23 GB though so I don’t believe its writing strategy of my drive.
Even if Verbatim BD-R aren’t the best, they (for me) have given very satisfying and even quality, I’ve burned maybe 100 from different batches and never had a single coaster that I remember. I use cheaper Verbatim, with CMCMAGBA-or whatever mid, for TV- and movie backups, and more expensive Verbatims with verbatim MIDs for backups of photos and stuff. For fun I sometimes buy other brands but I can’t be bothered to check quality as thoroughly as I used to do. Have like 5 50GB TDK BD-RE, they work great, but I haven’t dared go to BD-DL for backups yet, they might play in my machine but I have no other machine to test on and DVD-DL wasn’t reliable so…
As I mostly use OS X these days, and virtual Windows won’t let me do disk quality scans (I can check read speed though), I rarely scan for quality except Photo and home video backups. Back in the days I used to scan most disks right after buring them.