I believe they are as good, or as bad, as each other. The output depends on the encoding variables and not on the nature inherent to the codec. What codec you choose has an effect on the quality - MPEG can be mpeg 2 or mpeg4 for example. AVI files can even be an MPEG standard codec. DivX for example is (or at least was) based on the mpeg4 codec. DVD's use MPEGs, mpeg version 2 I think, as do VCD and SVCD, the only difference between SVCD and VCD is the encoding. SVCD have a higher resolution and a higher bitrate than VCD and so look better, although take up more space, for obvious reasons.
If you are interested in encoding anything into a digital form, I recommend the site www.doom9.org.
It's called itself a DVD Backup resource, but it contains a lot of good guides, and links to a lot of useful software that you might like to play with and see what you like best.
Hope this answer makes sense, it's been a while since I played with encoding anything, so I might be rusty on the details.