Hi Angliholic There is potentially a very big difference between for and on in that sentence. Using for tells me that Festivals International has given the name "Best Event in the World that is held on October 31" to the event held in New York on October 31. As your sentence is worded, using on suggests that Festivals International itself did something on October 31.
New words, one handy idiom, and a 2-minute quiz — delivered to your inbox to keep your streak alive.