Any would be legal subject to local bylaws. Business Plans probably offer you the best system performance BUT please risk assess and assess how suitable Dropbox is for this - Dropbox is NOT a backup tool, its not intended for that although it does it as a sideline.
For example, if you also store files locally and they are deleted/edited the cloud version is also edited. Thats not how backup systems should work.
- - - -
Did this post help you? If so please mark it for some Kudos below.
Did this post fix your issue/answer your question? If so please press the 'Accept as Solution' button to help others find it.
Did this post not resolve your issue? If so please give us some more information so we can try and help - please remember we cannot see over your shoulder so be as descriptive as possible!