I very much doubt that the extra cost and incovenience of getting a visa in advance would ever be worth it if you qualify to get one at the airport on arrival (which you will as, I presume, a US citizen going on a short holiday in Turkey).

Usually it's pretty quick, and generally I have arrived at the luggage reclaim area before my luggage has; occasionally there is a moderately lengthy queue but there are usually several people serving. Pay in cash, and have the correct change in US dollars (if you are a US citizen) for every passenger.

Despite one of the comments above, I have always found arrival formalities at Istanbul Atatürk Airport to be fairly well organised. Just don't get into the queue for passport control (immigration) before you have bought your visa, or you'll have to go back and start again!