I spent a whole lot of time comparing cloud storage systems to back-up my several computers and I finally chose Livedrive for the following reasons:

-IT IS CHEAP. It is the cheapest cloud storage out there (like $3/month), and it's good! I got a 5 year back-up plan for less than the prize of an external drive.
-IT IS AUTOMATIC. No dropping your files, no clicking on sync. Just install it and forget it. It instantly and continuously watches and saves all the files and folders you want, even the ones you are working with at the moment. You'll never find anything safer.
-NO LIMITS. No limit on the number of computers you can back-up (I'm backing up one desktop and two laptops now with only one subscription), no limit on the server space you use (really!), no limit on file size.
-ACCESS ANYWHERE. They only have an app. for IPad but you can access your files with any browser and even stream music or pictures to any phone (although streaming music is a little lagged for me most times).
-SAVE 30 VERSIONS OF EVERY FILE. Have you ever modified a document and wished you could go back? Livedrive keeps up to 30 older versions of every document you back up. Just log in an download the version you want to recover.

It's the coolest subscription I've ever had, and has helped me recover precious documents several times already! However, I only got the back-up subscription, for a lot more money you can get a virtual drive which you can access from your file explorer on all of your computers.