I had a hard time voting between Flash and both, I went for both. Although both would be a maintainence nightmare, but there are still too many computer illiterates out there without the plugins for flash (unless they're shipping them with IE nowadays?). The speed isn't a problem really, and there are hardley any modem users left out there. Damn! I just changed my own mind, flash only.
Idea: How about a small HTML splash page which lists the recent updates (or a popup link on the existing intro page). Then slowdem users could surfer the forum and that page and only need to load up the flash site, when they spot something they like the look of. Plus you'd only need to maintain one HTML page (which could even be database driven with little effort). eh? eh? Well I thought it was clever. What do you think?
-Kev