Orbitz is great for the following reasons,
1. The fares are usually cheaper than most airlines, especially in markets where SW does not serve.
2. You get a booking on a large air carrier with your choice of connections.
3. When booking you can add frequent flyer miles through the major carriers.
4. Orbitz is very careful in making sure you recieve all of the information on your flight, including delays. Orbitz sent me a Email on my phone on a trip through O'hare to tell me of a gate change, it saved me a long walk on a tight connection.
5.You get free gifts from Orbitz, I got a Zagat resort guide free of charge just for booking!
P.S. It is a good Idea regardless of how you buy your ticket, to check with the airline 24 hours before your flight to confirm your reservation