Personally, I back up to DVD-R myself and make sure than none of my backups are more than 2 years old. I know for a fact that the subtrates last considerably longer than that on name-brand media. My opinion is that those backup discs are more for post-emergency restoration than for truly archival purposes, so I treat them more like a first-aid kit than many people.
Going to Blu-ray would make more sense from the standpoint that they have a considerably higher capacity, but they are also still rather pricey (especially for the media), so I personally won’t be switching for a while.
I find hard drives, whether external or not, are too fragile for my tastes. If I drop a box of properly stored optical media, no problem; the same cannot be said for a hard drive. I would not store them in a spindle pack, sleeves, or normal jewel cases if I really cared about the data; they tend to scratch things. I have a nice hard-case that I could drop down a flight of stairs without losing a bit. I also tend to make two copies just in case.
As for any sort of online and/or cloud solution, I would not use that method to back up any data that I would not be willing to post on my Facebook profile.