Going with New York City, because the summer is not as long lasting as Barcelona. Yes, July is hot, but by the middle of august it usually starts cooling down at night and by September the weather is ideal. Barcelona hits 100 F far more often than New York City does.
An average low of 68 in September is just UGH
. NYC is much more comfortable with lows in the 50’s by then, and only has such hot lows for a day or 2.