The overall bit rate does more to determine how your video looks than anything else. These samples show you the trade off between file size and quality. All of these were compressed using the same 30 second Quicktime file sourced from a high definition master and saved for the iPod.
56kbps h.264
File Size: 612KB
128kbps h.264
File Size: 788KB
256kbps h.264
File Size: 1.1MB
256kbps Flash (Sorenson Spark)
File Size: 1.1MB
256kbps Flash (On6)
File Size: 1.1MB
256kbps Windows Media
File Size: 1.4MB
These clips use a javascript called ObjectY to simplify the code used to present the movies.