You might as well as which religion is best.
Seriously though, I look up prices at Travelocity (now that it offers multiple airport lookup). ITA Software (
http://www.itasoftware.com ) is in BETA right now, but it is going to offer something like that too.
Once I get my prices, I go to CO's website to book.
When I get close to departure, I go to ITN to see what my upgrade chances are.
Glad I could clarify the picture for you.
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"I will not be pushed, filed, stamped, indexed, briefed, debriefed or numbered. My life is my own."