The official decision is based on the sinclair formula. It's designed to create a total that can measure lifters across weightclasses, and the "best lifter" at a meet is the one whose sinclair total is the highest.
At any particular meet it could be any one or combination of your choices, but the way it's figured is here: http://www.iwf.net/iwf/sport_org/wei...t/sinclair.php
It's kind of like a mathematical way to figure out best kilo for kilo lifter.
Also, somewhere in my training log I did some work with it, and might have a better link. I know you can get an excel ready version of the formula.