What is the difference between cssSelector Xpath and which is better with respect to performance for cross browser testing

Question

I am using Selenium WebDriver 2.25.0 to test the content of a multilingual web application (For different languages like Arabic, English, Russian & so on).

Make sure that my application is the best one in terms of performance and that it supports all browsers (i.e. IE 7,8,9, FF, Chrome etc).

I appreciate your valuable advice in advance.