in xml you have a format of file that has url and some attributes, like creation date, rate of update, etc. in html you just have the links.
html is the readable format of the sitemap by people visiting the site while the xml format is for robots from the SEs and directories. You should have both and a JSON one as well
Check this sitemap.xml vs sitemap.html etc. article. It explains and shows differences between rss, xml, html, xhtml sitemap files etc.
In html format you can create links according to option and needs. But xml this is very time consuming and not easy to done. Manually you have to west lots of time to done it. You can also get more details by Google search, Just Type you Q? and you get the results in details.
sitemap.xml is for search engines. It lists all the pages you want SE to index. You may set priorities, notify how often page is updated and when page was last modified. sitemap.htm is for people that want to see a bird's view of the whole site or suffer from your crazy menu. If your site has hundreds of pages you don't need to list all - show just the most popular ones, not more than 100.
sitemap.htm is for user that want to see a whole site links sitemap.xml is for search engines. use for indexing . notify how often page is updated and when page was last modified. both are helpful for a site thanks with regards
XML Sitemaps are a standard, a technical agreement between the most important search engines including Google, Yahoo and Microsoft. HTML sitemaps are actually an HTML page with some links to internal pages. There's no real standard.
XML is the formate used for the secured data transfer and the same is with sitemap.XML but in the case of the sitemap.html it is not like that its just a static content display Thanks