Sadly backups aren't one-size-fits-all as the right solution for one person may not right for another. But here are some of my experiences which may help in deciding what to do:
Backup up to optical media is okay, but after a few years the discs may be very hard to read and some data loss may occur. I don't use optical media for backups anymore.
A RAID array will protect you from a single drive (dual if RAID 6) drive failure, but won't protect you from accidents, viruses, fire, theft, or malicious intents of others.
A local offline backup will protect you from drive failure, viruses and accidents, but may not protect you from fire, theft, or malicious intents and won't have the absolute latest edition of the data.
A remote backup will protect you from accidents, fire, and theft but not necessarily from malicious intents.
A remote offline backup will protect you from a lot, but the data may not always be up-to-date.
The cloud can be expensive, unreliable, or unsafe. (And for those who quote flat-rate unlimited backup offerings, not everyone can make use of those offerings otherwise the solution wouldn't make fiscal sense. You also don't know how well they will protect your data and Murphy knows that your local copy will die around the same time that your 99.99% reliable cloud provider loses half of your data.)
(Note that I consider 'offline' not just to be unmounted, but actually physically disconnected from everything.)
Personally, I have a RAID array for local safekeeping against hardware failures and I have and offline storage system at a relative's house which I update a few times a year to protect against environmental, accidental, virus, and other problems. For really important things I get, between when I put on the main array and when I do my offline Sync, I'll typically keep the original media around, just in case. There are some holes in my personal backup system, but it's good enough for my needs and doesn't cost that much.