As a pilot myself I can tell you that in EP there are really only a handful of criteria you look for when determining a place to land:

1. Minimize risk of ground personnel 2. Minimize obstructions between air and ground (ie. poles, trees and wires are bad) 3. Maximize straight and flat ground 4. Maximize featureless ground etc...

Given where Newark is, and Sully's flight condition, there was really only one place that would show maximum differentiation in human density and allow for landing: Hudson. The trick is knowing how to land on water with *a passenger jet - something remarkably simple to compute given environmental parameters (CG, load, wind, etc...) and a few simulations.

As was rightly pointed out, the key to success here was calm - something Sully learned starting at the USAF Academy (I'm a fellow grad as well, shout out where you can take it!) and was what let him do computer level calculations so quickly.