What is the difference between function expression and function definition in relation to Hoisting in Javascript?

Question

What is the difference between function expression (named or unspecified) and function definition in relation to Hoisting no Javascript?

Named function expression syntax:

var somar = function somar(a, b) {
   return a + b;
};

Function expression syntax, better known as anonymous function:

var somar = function(a, b) {
   return a + b;
};

Syntax definition of function:

function somar(a, b) {
   return a + b;
}

And where it is most recommended to use each of them?