I haven't been in the city in a long time, though I do visit the outlying areas - there are some beautiful release spots in Tarrytown and Sleepy Hollow! If I were to visit the city proper, I'd look for scenic statues, ideally with benches nearby - but I'd also look up the Little Free Libraries. (There seem to be quite a few on the LFL map, though some might no longer be active.) I don't get as many JEs from LFL releases, but I still like to use them.
Places NOT to release: anywhere with possible security issues, such as near government buildings. And if you're in an area where there are lots of sidewalk vendors, I'd be cautious about dropping books - they could wind up on the sale tables. Though one might get a catch that way; who knows?