Moody's has a nice quantitative analysis ranking the choices, but they also write up a qualitative case for each.
I like the qualitative approach better, as I think many of the critical qualities can't be quantified. It's not the best approach to simply average the categories, because obviously some criteria are more important than others. For a business as reliant upon the quality of its knowledge workers such as Amazon, cost considerations need to be secondary to which city can provide the most talented workforce available. It's also not the best idea to look at the data and simply compare cities based upon the percentage of college-educated workers. Amazon needs the absolute cream of the crop and that's harder to quantify.
I can really only see the Northeastern Corridor cities of Boston and New York being chosen. I think Amazon needs to be located a in true destination city to attract the best of the best, and my preference would be New York as it's a giant business cluster and it houses so many Fortune 500 companies and is located near so many Ivy League schools that it would be easy to find the best and poach the best.