If you use the google webmaster tools, they make you add a sitemap in XML which only the spider can read I guess. But if the spider picks up your sitemap from your website to index those pages, it is usually in html or whatever code you use.

I know in my case, I have used both. Many of my sites, I did a manual html sitemap and all the pages where indexed in a short amount of time.

But when I am lazy or in a hurry, I go to one of the free XML sitemap makers and then go submit it through the webmaster tools.

In my case, though, it didn't index any faster. It was just the work involved was faster. Oh and don't forget the XML version does not help your readers. They can't use it as a directory to your site.