I voted for HMTL, but my actual answer is more complicated than that.
I'd say that if you're a flashy media type, trying to sell your flashy media wares, to support your flashy media business, then Flash is the way forward - marketing idiots with deep pockets, big chequebooks, and little understanding of or care for accessibility are likely to be impressed (provided you do it correctly) and will (maybe)[1] pay you good money as a result.
If, on the other hand, you're trying to make your content available to as wide an audience as possible, and
if you care about making your site accessible to people with additional needs (screen readers, clear fonts, etc), and
if you care more about quality of content than you do about your own perception of what other people think is 'fun', then I would suggest staying away from a wholly flash web site.
People will find 'fun' in a well constructed, well thought out, well designed, site with good content, that is relevant to them.
If you build it right, they'll have 'fun'.[2]
[1] This post does not constitute any promise, either by the author or his family or agents, that 'marketing idiots with deep pockets, big chequebooks, and little understanding of or care for accessibility' will be prepared to pay you money, 'good' or otherwise. Any failure on your part to persuade those 'marketing idiots with deep pockets, big chequebooks, and little understanding of or care for accessibility' to part with their cash is entirely your own. The value of my interest can go down as well as up. Any likeness of characters in this post to persons either living, dead, or made out of cheese, is entirely purple monkey dishwasher.
[2] This was as close as I could get to 'If you book them, they will come.' - you get the point
