A combination of each is the most optimal solution
I've learned the hard way with hard drive failures (including a RAID setup going down, It has been years since that as drive space has gotten cheaper and bigger so I forget the number, The one which is most used for backup use).
I mean it is easy to have a backup of absolute essentials on one's self with the size of USB 3.0 small sized flash drives getting huge! Is it Kingston whom offers a 512GB one currently and will soon offer a 1TB model?
I'll probably pickup one of the 512GB one's myself once the 1TB versions are available. So I'll be able to keep all my most important files in my pocket or rucksack at all times and it'll serve as yet another backup as well as being an extremely practical way of taking stuff to and from other places I take my work to and pickup other's work on projects, collaborative stuff...etc.
So it'll be essentially just an extra offsite backup. Once the price goes down further and storage size increases then it'll be a no-brainer to add more and eventually replace the current slew of big capacity but still moving parts based (read and write head thingy) hard disk drives
Cloud storage is also very, very handy for taking stuff anywhere one goes but it has just the one problem; Being dependent on how fast an internet connection is to have quick access to stuff when not at my own place. Really so far that is the only problem I personally have had with cloud storage with fingers crossed
Cheers
