In one of Matt Cutts' videos on SEO questions, he answers a question about if you should build an HTML or XML Sitemap. An HTML sitemap is an old school landing page for users to find all (or most) of your pages on your web site via single page. In many cases, for large sites, a site would require many HTML sitemaps to make this useful, but for smaller sites (see RustyBrick's sitemap), it makes sense to put everything on a single web page. An XML sitemap can also be multiple files, but they are not visible to a user, only a search engine spider.
When Matt from Google was asked if you had a choice, which one would you pick, he picked an HTML Sitemap because both users and spiders can chew on it. I am not sure if most SEOs would make the same selection, but this person didn't ask an SEO, he asked Matt.
Here is Matt's video:
As Matt said, once you make an HTML sitemap, making an XML version is extremely easy. So, my advice, do both, if possible.
Forum discussion at DigitalPoint Forums.