SugarSync

My experience with SugarSync has been extremely positive. The most outstanding feature is its flexibility. Unlike other cloud services that force you to put everything into a single “magic folder,” SugarSync gives me the freedom to sync any folder directly from my computer. I didn’t have to change the way I work — instead, SugarSync adapted to my workflow.

In addition, it always gives me peace of mind. Its Protected Folders feature acts like a digital safety net. Even if I accidentally overwrite a file, I can easily restore its previous version.

Most importantly, all my essential files — whether they’re on my office laptop or personal desktop — are always up to date on my phone as well. I can truly work from anywhere. It might be a premium service, but the convenience and security it provides make it worth every penny.

The bad news. It doesn't always seem to spot that a file has been changed, so if you absolutely have to rely on it then go elsewhere (I wish I could recommend somewhere)
The good news.
No special sync folders, you just select the folders you want to be synced. (eg My Documents, \users\me etc). In our household we have Desktop, HisLaptop, HerLaptop,ChildLaptop. MyDocuments on each laptop syncs to Desktop\him desktop\her desktop\child. And so on for various other folders. Now if I create a new file, edit an existing file or even delete a file then that change is uploaded straightaway (ish) to the SS website, and then gets pushed down to the synced folder. Perfect.
As a bonus you can create a link to a folder (eg HolidayPhotos) and send that link to the interested party (eg grandparents). It costs me about 70$ a year for 250G.
It's a bit of a hog on starytup, after that you don't really notice it's there. I would recommend it to anyone,IF ONLY IT WORKED ALL THE TIME. But it %^&*( doesn't