I vote for HTML
There are a couple of useful features in flash that I have noticed and, true to what has already been stated, these are features that deal with graphical display. For example, maps and technology data. For search purposes, navigation and introduction, Flash is a complete waste of time and bandwidth.
A solid rule to stick with in web design is that providing the information quickly and clearly is paramount. A user should not have to think about how to find the information (navigation) and he/she should not be delayed from finding the information (introduction). For these purposes Flash does not add anything.
As a number of respondents have commented, Flash intros are usually skipped and they don't actually provide any useful information. As for navigation, that seems to be rather tricky in Flash. I have seen a few sites where the logic of navigation just frustrates the user. There's a strip club that comes to mind. They use Flash for navigation.
As for the option of Flash/HTML, that seems to be like the old frames/no frames option offered by some. As far as I'm concerned, go with either one or the other. Invariably, there are huge differences in the amount of work put into the site and one or the other versions (most likely the HTML version) will suffer for it. Again, I've seen this done a few times.