It is better to use CSS with Master pages. Once your master page has been created then it is easy to maintain your codes. If you are not satisfied with a shared content, such as header or footer, all you have to do is modify the Master page and the modification would be reflected across all pages that you have applied the Master page to. Whenever you add a new page to your website, you will get an option to apply any Master to the new page. You can have multiple Master pages in one web application to give different pages a different look and feel.