As of late (and i caveat this by saying i do two round trips a month)... i've been having fairly good luck.
I tend to take the 5PM train from NYP and the 6AM from BBY....
the other big thing to take into consideration... if the weather looks bad... just assume it's 10 times worse b/c every shuttle person runs to the trainstation almost immediately at the first sign of a storm in the North East.