I find DVDs do not hold enough to be useful. And they contain organic material, which is vulnerable to degrading. As previously posted, archive quality discs maybe be up to it, but they still won't hold enough data.
We use portable hardrives. Note the plural here.
With any system you use, its not a question if it will fail, but when. So we have two external drives. One for regular backups, and another stored at a relatives, which we occasioanlly take back, to back up all our music and pictures. etc.
A third alternative is blu-ray discs. These have two advantages over DVDs:
They hold far more (50GB)
They contain no organic material so less suseptable to degrading.
Haven't looked into the cost recently though.
Again, assume they will fail at some point.
The issue of having the tech to read said data can be easily managed if you keep it all in one place, and regularly back it up.