I'd say there is no best. Each of them composes different kinds of scores each suited for the things they have to compose for.
I must say though that John Williams has the most variated track record; space operas, adventure movies, horror, the man seems to excell at making brilliant and immersive scores for almost any kind of movie. So I'd pick him if I had to. Yeah, Danny Elfman is brilliant, but his scores always stay within the fairytale style (whether they're dark like Sleepy Hollow or Batman, or magical like Edward Scissorhands). Yeah Ennio Morricone is brilliant, but he's known for Westerns. John Williams though can do it all.
I am sadly disappoint of the lack of Hans Zimmer in your poll though. Really that man is a legend.