See: http://eslint.org/docs/rules/func-style

My personal preference is to prefer declaration style, as it allows hoisting (and just looks better to me). The only issue is when you want to reassign:

var func = function () {

}

if (someCondition) {
  func = wrap(func);
}

ESLint's func-style rule does not accommodate the above exception when preferring declarations, so it is impractical to enforce.

Note:

You can get around ELint's rule by doing this:

var func; // don't initialize variable here, do it on the next line

func = function () {

}

But that feels impractical.

Do we feel it's worth enforcing func-style in XO? Should we use the builtin plugin to do so, or make our own that is a bit more permissive.