In my opinion, if we consider this as a total stochastic process, the probability of no one choosing 100 is quite low, and 67 is definitely the best choice.
But actually, 100 is not really big enough, so maybe 67 is the best choice when there are 100000 or more people.
On the other hand, if the best choice does exist, I highly doubt that there is any better strategies than choosing 1. Suppose the best choice is X, and I'm sitting in the classroom of Harvard or MIT where everyone else is just too clever not to choose X, then the best choice in this particular case becomes X*2/3. Only if X=0 or 1 will this contradiction be resolved, and as stated above, 1 is better than 0.
Guessing only, anyone has better ideas?