I always use link. However, recently I've been organising my CSS files better. Now I have different CSS templates configured, and they import the CSS files I require. So I may have a CSS file called tables.css. That would load in my primary, secondary, and ternary CSS files for my HTML tables.
I would use <link>, and its because of some browsers like some Opera 9'ers and older IE'ers will first read then HTML structure and THEN apply the CSS and not the other way, so the website transform will be abit weird while loading =)