That is a question we cannot answer. It depends on your travels. I would get the Delta if you fly, well, Delta. I would get the Blue Sky, well, if you fly Jet Blue. If you fly both, then you will need to choose which one you fly more.
One more thing, AMEX has the best customer service by far, and I am sure they will be very willing to help you crunch the numbers as to which one will be the best for you.
I did a product change from the Delta Skymiles to the Blue Cash, and when I did the rep spent 5 minutes with me crunching the numbers to see which one would be the best. I have never had this type of service. AMEX rocks!