Electronic or paper? Honestly, it doesn't matter that much. Etickets can be purchased probably a few hours in advance. Paper tickets may need 24 hours to get ready, then they take 5 minutes to buy at an airport ticket counter. Just remember that when buying a paper ticket internationally, not every airlines' counter is open all day. You'll probably have to buy it at a US Airways counter, and at the international stations they're generally open only during check in time, roughly (generally in the morning).