The most important element you are considering (obviously all of these may be somewhat important):
methodology used in the school (traditional, developmental, competitive, progressive, etc.)
size of classes, number of teachers, advisory structure
logistics of neighborhood, and ease of transportation
criteria for admissions: testing, portfolios, etc.
afterschool services, early drop-off, extracurricular activities
Are you:
moving to New York City?
living in New York City but thinking about changing schools?
a new or adopting parent thinking about first school choices?