HTML vs Flash Design
HTML sites are websites where most if not all of the information on the page is static. You'll notice that HTML sites have different names for each page. HTML site are better for sites that carry lots of products and for site who's purpose is to be a the top of website rankings.
Flash sites are sites where content actually movies on the page. Rather than be multiple pages, flash sites are movies. Flash sites work well for smaller sites or sites that do not require strong standalone website optimization.
Sites can also be a combination of html with flash elements. If you are looking for a little glitz and glamour but need the marketing capabilities or flexibility of HTML, building an HTML site with some flash elements will give you the best of both worlds.
To decide what is best for you will really depend on the required functionality of your site and how much you are looking to spend in time and money.