The answer to this depends on the monitor resolution used by your site's visitors.
Screen resolution is a major Web design issue.
If you design your page for a high resolution monitor, visitors with lower resolution screens will have to scroll to the right to view parts of the page. This is done by defining the width of HTML tables used for page layout in terms of screen percentages. However, this gives less control over the position of page elements within the table. As a result many Web designers prefer to define their table width in terms of pixels. The conventional wisdom has been to design to the smallest screen width in common usage.