Coming to the comparison of HDD vs cloud for backup use, the most important thing in backup is redundancy. It is always better to have multiple copies if you really do not want to lose it. So, 2 is better than one. That can be done with hard drives. However, if you are going to store 2 hard drives on the same spot, you still risk that they will both be destroyed or stolen at the same time. So, that is where the cloud comes in. It makes it easy to store data somewhere else and most cloud storage solutions add redundancy themselves, because they really don't want to lose your data.
I would advice you to keep at least one HDD with the data in your own house for quick recovery and store a second copy somewhere off-site, be it with friend, your parents or kids. Someone you trust they will not go snooping around in your data and take good care of the hdd. Update it once a week or month and rest easy. If you go cloud for your off-site backup. I suggest encrypting the data with something like Truecrypt.
tl;dr: HDD is great, but store data off-site. Cloud makes off-site backup easy and relatively safe if you encrypt your data.