Backblaze B2 with Duplicacy here as well. Lately I’ve been looking at Azure and their archive tier storage as that’s way cheaper, granted with the rather obvious caveat of twice as expensive to pull things back from, but for the actual archival of stuff that I hope I never have to pull back that’s a bit moot.
The whole “SSD’s lose their data if they’re unplugged” is a bit of a moot point especially if your plan isn’t to bury it underground for centuries. That said personally I’d still go for HDD mainly because you get 4+ times the storage for the same price. If you only need a terabyte or so and the amount of data isn’t going to grow then sure, SSD works just as well.