It's easier to do fancy-looking sites with Flash - but that's not necessarily better.
It's easier to do functional websites with HTML, Search Engines like it better too.
The key question is what you want your visitors to do with your website.
At PhotoDeck (www.photodeck.com
), we do only HTML sites - but they're e-commerce photography sites geared towards image sales and delivery rather than portfolios. We have a partnership with A Photo Folio, as Jon mentioned they do flash for the time being, but they're clean designs and similar things could be done in HTML too.
In fact, one of our users is now planning to create another PhotoDeck website for his portfolio, it won't be fancy but there is something to be said for simplicity and performance...