It depends on so many factors, and the prevailing winds end up being a minor part of the decision. So I gather, anyway. My wife and i are heading E-to-W this summer, and all things considered, it's the right way for us.
Other considerations: Do you like to head out from "home", or end your trip in familiar territory? Where will you be in the hell-est part of summer? Do you tap into the "Corp of Discovery" feeling of a westward adventure, like the 19th century explorers?
Here's probably the best description i've read of the East vs. West decision:
Mark Gardner's journal. He gives his philosophy on the first page, but the whole journal is a good read.
Have a great trip, whichever way you go.
-- Mark