In Queens, about 13 km from Midtown, LaGuardia is the closest airport to Manhattan. It is primarily an airline airport and very congested: private jets need a prior reservation and have only one private terminal.
LaGuardia is a high-density airport: every private flight must obtain a reservation in advance, and slots are scarce at peak hours.
For a private jet, Teterboro or White Plains are usually simpler and faster. LaGuardia remains convenient for a connection with a domestic flight.