Definitely a tough one, but the more critical you want to be, the easier the choice becomes. Jaws boils down to having an interesting but rather bland premise, some nice direction and such with a music score that really captures the emotion more than anything else in the movie. Meanwhile, One Flew has more legs to stand on. Jaws beats out Cuckoo's Nests music, but loses in pretty much every other category. You could compare Bruce to MacMurphy, but who do you compare with the rest of the cast of OFOTCN? Jaws is a classic, no doubt, but I think this is the round where we'll have to shoot the barrel and knock it out of competition.
One Flew Over the Cuckoo's Nest.