Lots of codec questions have been flying around lately with the release of Apple's H.264. I went ahead and made a wad of 10 clips using different codecs and encoders, with the same settings.
They're all 200 Kbps video only CBR, using the slowest, highest quality, 2-pass modes available. The content is very challenging, so none of them really look that good, but the differences are quite illuminating.
I won't prejudge things by saying what I think, but for those who are interested, here's the torrent: