Lately I've been noticing that when checking out I definately have a formula on how to pick a checkout line. If anyone else has insight please feel free to comment. Here are my criteria in order of what I think is important.
1. The number of people in line matters more than the number of items. This is why the express line is not always better. The more people in line the more idiots there are that need price checks or something like that.
2. Look at the cashier. Not to be ageist but younger is better. Too young is bad though because they don't know what they are doing. If you can, pick the line with the manager (s/he will be dressed up, most likely wearing a tie) because they tend to be faster and can resolve all problems without having to ask someone else.
3. Look what makes up the line. Often times what looks like a long line is not because there is an entire family waiting together in which case there is really only one customer ahead of you, not 5.
4. Look at the demographics of the people ahead of you. Again, not to be ageist or sexist but younger men are the best. They tend not to ask questions and they almost always seem to pay in cash or credit card. For whatever reason the older and more female =) you get the more likely you are to write a check or need something answered. Men hate writing and hate even more admitting they don't know something.
5. This will contradict one somewhat but all else being equal, the less items the people in front of you have the better. Just don't bet that the "express" lane is any faster because it usually has 3x as many people. You need to find the right balance.
6. Don't get behind a hot girl and a male cashier or any guys and a hot female cashier (unless you want to check out the girl). I swear there is much to much flirting going on in the checkout line. Yesterday I had a male cashier practically walk out with the hot girl to put the groceries in her car.
7. Check out at an alternate location. Places like Target allow you to check out in their Garden or Electronic section even if you aren't buying anything in that department. These lines are usually much shorter.