Depending on the savings of living with your SO in NYC, I vote Chicago. If you have a really strong preference to stay in NYC with the SO and it would be a significant COL savings, then that might be worth the difference between NYU and Chicago.
Fwiw, I tried to negotiate for more at NYU, got turned down, and emailed them again to re-appeal given my new Columbia offer and they put the appeal tab back on faaps. If you didn't have your Chicago offer before, I would definitely re-negotiate.
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