Altho' I'll stick with my first place vote for the N&W Class J, especially for steam, my second pick (and first place for diesel) would be the Alco PA-1 "Spirit of 1776", decked out in bright white with red, white, and blue trim. It pulled the seven car American Freedom Train through all the states (48 at that time) from 1947 to 1949. See http://www.freedomtrain.org for pictures and history.