Well, let's take a look at the numbers. There are 14.6 million Jewish people worldwide (5 million in the U.S.) as identified by the Jewish Year Calendar. There are 3 movements in the religion (sects to you Christians): Reform, Conservative, and Orthodox.
islamicpopulation.com states there are 2.1 billion Muslims worldwide, with an identified 7 schools of belief with 17 sects divided among them.
There are an estimated 2 billion Christians worldwide and we have, all under Christianity:
Catholocism, Protestant, Eastern Orthodoxy, Oriental Orthodoxy, Anglicanism, Restorationism, Unitarian Uiversalism, and Nestorianism. Since I mentioned Prostestant denominations specifically, there are 670 million Protestants, and they are divided between 5000+ denominations.
So, I don't know. You tell me where the most disagreement on schools of belief lies.