I have been using Dropbox to sync, backup, share and publish files for a few years, and I am still using it today.
Dropbox is pretty good, but it lacks of access control feature for sharing file/folder with other users. For example, you cannot make a shared file/folder read-only to your buddies, and you cannot prevent your file/folder from being deleted by your buddies.
I heard that Dropbox is now finally trying to introduce such collaborative sharing features, but they plan to limit the function to Dropbox for Business which is not free and requires subscription.
Meanwhile, Microsoft has evolved their SkyDrive into OneDrive and bundles it with Microsoft Windows 8/8.1 and Microsoft Office 365. When sharing file/folder in OneDrive, we can define it to be read-only (recipient can only view) or full access (recipient can edit).
There are other cloud based file sharing applications such as SugarSync, Box.com, etc. which also support for collaborative sharing access control, but such function is only made available to the non-free version of their service.
As such, I found Google Drive is so far the best cloud based file sharing applications in terms of feature, particularly on collaborative sharing access control. Besides, you get a free cloud storage of 15GB (shared with Gmail and Google+ photos) with Google Drive, compared with the 2GB initial free storage in Dropbox and 7GB free storage in OneDrive.
You can activate your Google Drive service if you have a Google user account. All Android phone/tablet/device users should have one, and if you are using other Google services such as Gmail, Blogger, etc. you also have it.
You can access Google Drive by browsing to https://drive.google.com. One that page, you can download and install Google Drive sync service into your computer.
Google Drive app for Android can also be found in PlayStore, and Google Drive for iOS can be found in Apple iTune Store.
The Google Drive installation process for PC is pretty simple and straightforward.
You can set the file/folder access control the moment you share it out with Google Drive.
Your buddies can even make comment to your shared Google Docs files.
And you can define if your editors with the "can edit" permission are allowed to add people and change permissions or not.
The table below shows the access control mechanism of Google Drive, which is pretty comprehensive and similar feature can only be found in subscription version of other alternatives.