Amazon will pick a U.S. East Coast city to capture talent from NYC, Boston and D.C., and with an eye on Europe. This approach would best complement their Seattle HQ, which already attracts talent from west of the Mississippi and with an eye on Alibaba in Asia. 

Denver will be a contender but will lose out to a major urban, metro area like D.C. with many tier-one academic institutions to fill Amazon's pipeline. 

Besides, Bezos already has a presence in D.C. as owner of the Washington Post.