In Manhattan, any of the Midtown canyons are of course fantastic (though I'd say the
West 30s are generally the best of the best); but my real favourites are some of the broad, north-south residential canyons on the Upper East and West sides, especially where you get a view downhill:
https://goo.gl/maps/CAXQTXtRzFwGtFhH9
One of my favourite intersections downtown:
https://goo.gl/maps/gn5bP6z3xGqgDr1V7