People who blog are full of opinions. You have to decide which ones are worth your time. I was just reading some c|net comments about hard drive backups. Some people hate the companies whose hard drives failed for them. Some think hard drive backups are great. Some hate the backup software. Some hate CDs. Some love CDs. All have opinions.
Why backup to a hard drive? Simple, your hard drive will fail at some point. Having a separate hard drive gives one more chance. Probably both will not fail at the same time. Cost is always a factor.
With one backup method only, I would choose online backup.
The cost is probably about the same as your hard drive or CD collection.
Online backup gives you a copy of your data in separate location. That online service will have multiple backups of all their data, giving you even more protection.
Your main danger with online backup is the company could go out of business. Usually, you get some warning, giving you time to move to another provider.
The odds are better with online backup. The cost is roughly the same.
Whatever you do, set up automatic backups.