Depends on the size of the site, but if you have a bigger site it is good to use xml for google and html for users.

xml sitemaps just make it easier for search engines to find all your pages, and allows you to hint priorities for crawler returns. HTML sitemaps are just for visitors, to make things easier.

Both. Neither.

Apples. Oranges.

In other words, they are different things, and so they can't be compared.

For what it's worth, this is Matt Cutt's view on this question:

YouTube - Which is better: an HTML site map or XML Sitemap?