If you work on more than one computer, you do not want to guess where the latest file is. That is why I once wrote about Syncplicity. You chose which files or folders to keep current, and synchronization largely happened automatically. At the time I compared storage allowances and monthly prices. Those figures are no longer useful buying advice.
What must stay in sync?
Start with a list of files you need on several devices. Not every folder belongs in the cloud. Some documents are for you alone; others are for a team. This determines who may view, change or share them. If two people edit the same file at once, you also need to know how version conflicts are resolved.
Syncplicity's current documentation focuses strongly on business collaboration. It describes folder synchronization and version management. Specific functions depend on the edition. That is a better comparison point than an old promise of a few gigabytes of free space.
Test a real situation
Create a test folder, edit a file on two devices and see what happens. Check that someone without access truly cannot open it. Automatic syncing is pleasant only if you understand the exceptions: offline edits, deleted files and shared links. That keeps convenience from becoming confusion.