Re: Which cloud storage?
Most of the issues have been covered but it should be remembered that even if you have a good fibre connection the upload speed to a cloud store is pretty slow compared to a USB connection.
However there are a number of free sites which are probably not going to go broke (Google, Outlook etc) but you can always use several on the theory that they won't all go broke together.
If you are worried about the security of your files you can always encrypt them before uploading them which is pretty simple - eg putting a number of files in a zip file with a password is probably the easiest - depending on what they are it might even make them smaller and hence quicker to upload.
There are specific programs for encoding individual files (
Click Here for free example) but don't rely on the passwords in programs like M$ Office as they are not secure.
Don't rely on CDs or DVDs for long term storage because the dye used in them has a limited life (and they are easily damaged).
If the stuff is really important you might be better invest in a NAS system which has RAID redundancy ie makes a couple of copies of each file on different hard drives at its simplest.
BUT with any backup it is pointless keeping them next to the computer that just ensures that they both go together in event of a robbery or fire.