FWIW - I do not save anything to CD's or DVD's. I have a bad track record with losing data on DVD's or CD's.
If you choose to use CDs or DVDs:
CDs are significantly more reliable than DVDs--they have a lot more error correction. (DVDs are designed for video where a few bad bits don't have much effect.) Write-once CDs also have better long-term storage properties than rewritable CDs.
CDs are cheap: make two (identical image) copies of each CD. That way if you have a problem with one, you might be able to use the second copy or assemble a good image from the two copies. You can also store them in different places.
One should also stay away from proprietary data storage formats. Otherwise you can lose access to your backup data when you upgrade your OS and discover that you can't get a version of the backup software for the new OS version. (Open source software is safer than proprietary software for this issue--if necessary you can upgrade it and compile it for the new OS version.)
For long term storage, one should occasionally make new copies of the backup media. (And there is also the risk that at some point in the future, the ability to read a medium or its data format may be lost. (Don't laugh--significant amounts of valuable data have been lost this way. IIRC, there is a last hour initiative on to rescue the Apollo Moon mission data.)) I don't know the expected lifetime of a CD.
Also for
any backup strategy, check it by reading back at least some of the data. Many a sysadmin has discovered to his dismay that he couldn't restore from his backups... (I used to manage and sysadmin a group UNIX computer facility--we did daily backups to tape and, yes, we checked them.)
I personally backup all my data to a mirror disk using rsync (*NIX only).
Doug