Some time ago I wrote an article: Dropbox vs Copy: Copy offers more free space and after some testing and daily usage, I prepared this comparison table.
|Windows, Mac, Linux||Yes||Yes|
|Bandwidth Limit||Yes||Yes*||Dropbox has an additional option: "Limit automatically" for upload (I don't know how it works)|
|Manage shared folders||Yes||No|
|Search Function||No||Yes||Sadly, Copy has not yet a search function (which I think it's very handy in Dropbox), so you will have to browse all your folder structure to find what you need...|
|Download entire folder as Zip file||Yes||Yes|
|Move files into another folder||No||Yes|
|Versioning||Yes*||Yes||*In Copy.com you have to click the file, then on "File activity" to see the older versions. In Dropbox it's more user friendly: you click directly on "previous versions" and you can directly restore to an older version (which is not yet offered in Copy.com)|
|Restoring deleted files||No*||Yes||*Copy.com doesn't allow yet to undelete files via web client. Recover deleted files with the desktop client|
|Sync speed||Fast||Slow||Maybe it's just my impression, but Copy seems faster than Dropbox.|
|Share a folder and let people add/remove files||Yes||Yes||Invitation sent by email|
|Copy a shared folder to your account||Needs a few minutes||Instant||Copy seems buggy: it creates a folder and it's empty. Only a few minutes later you will see your files... so don't worry, be patient.The button "Save to Copy" is available only when you are logged in and it is displayed at the bottom of the page, like in this screenshot:|
|Space used when sharing||Shared between peers*||Counted the same for each person||*With Copy, if you share a 2GB folder with 3 friends, "Copy" will count 500MB (2GB/4) for each person. With Dropbox, every person will lose 2GB from his/her account|
|Free account||15 GB, 20 GB with a referral||2 GB, 2.5 GB with a referral|
|Maximum free size||Unlimited (!)||18 GB :(||With 8 people using my referral link I already have 60 GB (thank you!)|
|Bonus / referral system||5 GB (!)||0.5 GB :(|
Feel free to comment. I may update this table as soon as I discover new features or relevant differences.
Conclusion: it seems to me that Copy.com is the most generous service available (unlimited space offered for free, and 5GB for each referral). I just canceled my crashplan account and didn't renew my flickr pro one. Why paying when I can get my backups hosted for free?
However, if you need a better support for versioning and undeleting files, I recommend you to use Dropbox for that. I use both. Dropbox for my little projects (source code doesn't require a lot of space) and Copy to save my entire collection of pictures and videos, which needs a lot of space.
Check also my post on How to use Copy to backup an external hard drive.
Note: I will remove the referral links in the comments, so please do not put them. Thank you.