How to choose the fastest line at the supermarket

Murphy's Supermarket Law states that whichever checkout line you choose, it will be the slowest. However, the folk at Lifehacker have come up with a rule of thumb they reckon will give you a faster through time:

When choosing which line will be the fastest, it might surprise you to learn that the "express" lane may not always be the best choice. Meyer took a scientific look at supermarket checkout times and came to the conclusion that the number of people in line adds more to the wait time than the number of items each person has in their cart.
[W]hen you add one person to the line, you're adding 48 extra seconds to the line length (that's "tender time" added to "other time") without even considering the items in her cart. Meanwhile, an extra item only costs you an extra 2.8 seconds. Therefore, you'd rather add 17 more items to the line than one extra person!

A rule of thumb I learned years ago for McDonalds and other fast food joints is don't choose any line where an adult has children.