Interesting question. Since you ask which goalie has best chance of being a top-5 in the world, that's a totally different question than which will be the best of the bunch in 5 years. I really like Binnington and think he has a very good chance to become top 10-15 in the world. However, Husso has a much higher ceiling because of the physical skills. Same could even be said of Copley. However, I think those 2 have a much higher bust potential. Husso may have issues adjusting to the NA game and there have been rumors of partying too much. Copley has had one good season ever in a back-up role for a good team. As for Allen, I have no faith in his big game ability. I am voting Binnington but I think top 5 in the world may be pushing his potential. So I wouldn't argue with Husso, or ....Husso.
Edit: Dangit. Since Husso was last thing I typed, his name was my mind I accidentally voted for him. Maybe a Freudian slip of the fingers.