lorax - 7:39 pm on Mar 22, 2012 (gmt 0)
If you modify your header.php file to use if/then/else logic then the processing is done on the server and is pretty quick. The comparison can be done based on page names/id numbers. The disadvantage is that you'll be making HTTP calls for each different CSS file unless you cache them.
A good question to ask is do you really need a different style sheet for the different pages?