Windsor knot. Perhaps it was due to a cautionary sentence by Alan Flusser - the de facto style reference for many men today - in one of his books or perhaps a source I have now forgotten. Whatever the original source, I had always assumed a small, neat knot was the preferred choice - namely, the four-in-hand knot.
Nonetheless, I still harbor a slight reluctance to tying very thick and wide knots. You need some extra gumption to pull that off (a la Robert Rufino).