ffdshow has been known to introduce artifacts in some things on rare occasions (usually when badly supported codec options are used).

Playback is a tradeoff: ffdshow is easy to use and good for slow machines, but isn't perfect (most people can't tell the difference most of the time anyway though). Using the actual codecs (divx, xvid) gives you better image quality if your computer is fast enough to use the codecs, but isn't slow computer friendly and requires more work to keep updated.

DivX player probably just uses the DivX codec for everything, so that might be your difference there.