Best online storage make things easy. On the opposite, some online backup services try to keep their customers by locking their data.
Data lock in prevent customers from changing providers, because they are not able to move their data from their online storage.
What you need to check in your contract is that your data won’t be locked in, and will sometimes organize data migration to another provider.
For instance, the online backup list published on best-cloud-storage.org does not include any providers which could lock your data.
Cloud storage terms of service
Boring but very useful when you have to choose the best cloud storage, you need to read the cloud storage terms of service.
Things to check for instance : are Data Centers geo redundant, which means your data is stored in different location to prevent nature disaster.
Another thing is to be sure your online data is encrypted with a key stored in a different place, to prevent hacker attacks.