The latest Seorountable blog post is talking about why HTML sitemap is better than XML sitemap. Here is a video in which Google's Matt Cutt answers SEO related questions and preferred HTML sitemap over XML sitemap.
But if the site is small and has less pages, then it can easily use an HTML sitemap for putting everything at one place. It is the oldest way of landing on the search page. Whereas, the XML sitemap can have multiple files but are not visible to the users.
Matt Cutt tells the reason of choosing an HTML sitemap by Google is because both the users and search spiders can follow it for important information results. The other benefit can be that it becomes very easy to make XML version after creating a HTML sitemap.