Personally, I have trouble picking the right codecs. I want to pick a codec that a person can use without downloading much of anything, or searching for a codec pack. I used to use Sorenson 3, but I found out that it can be too large a file format in some cases.
After much searching windows media codec has gotten me. The options are very easy to set and tweak. I am also capable of getting at some elusively small file sizes, and still having my video render to a good enough quality. That and you know its gonna run on every single windows machine.