I choose Flash over HTML5/javascript at the moment because
It sucks to not reach half of the visitors or inconsequent result between browsers that I have to test manually.
I need to convert to different formats manually and multiple versions. Compare to Flash that I have raw formats and on the fly compress all to a small single distributable file.
Flash show speed with AS3 and flexible API for optimization, bitmapcache flag, antialias-control compared to javascript with no type-definitions, lack of features that have to be written highlevel (and slow).
Flash is more fun. Mature API for graphics, sound and text. Quick development.
HTML5 is just a tool in the bag. It add features but not replace others.
