Your data backup strategy should try to solve the problem of:
- any changes, no matter how small. This should happen daily, and account for files added/updated, or deleted. This solution should ask you whether to track them all, or a specific filetype. (documents, music, video, pictures)
- recovery time. Not only should it be easy to mass recover an entire drive, but also just ONE file that was changed/erased accidentally. Online solutions will be a long process for when your disk dies and you need to fill in the new one.
- offsite backups. This could range from burning DVDs with static content (movies that are done and won't change) and keeping them at Grandma's house in the basement. We all have heard the stories from people on the news whose house has burned down that they've lost everything. Consider an online solution whereby you have an account that will do the synching for you as well. Cost becomes a factor.
The value you place in backups is typically your deciding factor. The online solutions typically cost money, and it's up to you to determine the value of that service. Otherwise, consider burning a few DVDs and storing offsite every 6 months. Perhaps a second removable HDD will work in a rotating fashion; go to Grandma's house and swap out the old HDD for the new one; repeat every 6 months. That will ensure your offsite backup is fresh enough in case of a theft or fire.