Here's an article about CSS Selector specificity which looks good: http://www.smashingmagazine.com/2007/07/27/css-specificity-things-you-should-know/
The section in How to measure specificity? gives you the answer:
a:link => one tag (a) + one pseudo-class (:link) = 1 + 10 = 11 points
ul li a: => three tags (ul, li, a) = 1 + 1 + 1 = 3 points
So the a:link style wins.
Hint: Order (in the CSS files) only matters when two css selectors have the same specificity.