Flash 8 also supports On2 [w]VP6[/w]. Since Macromedia decided to include it after including H.263, we can probably safely assume that it is ‘better’ in some cases.
Tinic seemed to like it, anyway: http://www.kaourantin.net/2005/08/quest-for-new-video-codec-in-flash-8.html
(Although now (as of one of the FP9 updates) H.264 is included along with H.263 and VP6)
