I have to write a web application for a client soon. Looking at the specs, there is no reason why the project couldn't be an HTML5/CSS/Javascript project, but the client is arguing that it has to be Flash.

The project has a number of dynamic elements and is web-based. It'll only be used in-house by a small number of people and all of those people use either Google Chrome or Safari 4. They are all pretty tech-savvy to boot.

My question is this: what are some of the reasons (preferably technical since this is Stack Overflow) I can present to my client as to why HTML5 is better than Flash (that's assuming I'm right and it is in this case)?

Is it OK to use HTML5 even though it's still a draft spec (I'm assuming it is after checking out all those Apple HTML5 demos a few days ago)?

Also, would a hybrid approach be preferable for now? Something that uses Flash wherever the canvas object would've been used in the HTML5 approach and that conforms to a normal XHTML approach.

Help!