For my library (to say nothing of all my other stuff) no free plan is enough. I've used various cloud servers, both free and paid, over the years, but Dropbox suits me best. It's one of the oldest and best known (I've had more than one cloud provider go defunct during the past 12 years), and as I actually need several TBs for all my stuff, I don't care that Dropbox has no smaller plans. It's also one of the fastest among those I've tried (some cloud servers were exceedingly slow) and I've had no issues with corruption or data loss.
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