For the green line that goes downtown, the lines at stop #1 can be LONG. Try getting on at stop 20 or 21. Even better, do the purple uptown tour for $10 more, and change at stop 38 (=green 19)
To leave a comment of learn more about the bus tour, visit the Reuters Business Traveller page. http://travel.uk.reuters.com/locations/new-york/info/gray-line
Watch out that the CitySights buses will try to swindle you onto their buses and make you pay extra fee. A total different tour company from Gray Lines!