document relative links.
Its all about personal preferences, but personally, I much prefer working with site-root relative links than document relative links.
Because you are dealing with absolute paths rather than relative paths, you know where everything is.
The only 'problem' with this method is when using php includes, which can't find files referenced by a site-root relative link, so you need to use an alternative. (document relative link, or virtual(), or $_SERVER['DOCUMENT ROOT'] method).