Functions that return a variable

I'm simple looking for what the general preference is between the below options:

-
anon function directly to variable

middleware.customer = function(req, res, next){
    req.customer = function(){
        var customer = false;
        if(req.method == "POST") customer = req.body;
        if(req.method == "GET") customer = req.query;
        return customer;            
    }();
    return next();
}

-
raw build variable up

middleware.customer = function(req, res, next){
    req.customer = false;
    if(req.method == "POST") req.customer = req.body;
    if(req.method == "GET") req.customer = req.query;
    return next();
}

-
complete separation

var customer = function(req){
    var customer = false;
    if(req.method == "POST") customer = req.body;
    if(req.method == "GET") customer = req.query;
    return customer;            
}

middleware.customer = function(req, res, next){
    req.customer = customer(req);
    return next();
}

I think B is the best of the three, but here's another alternative using a simple lookup:

middleware.customer = function(req, res, next){
  var methods = {POST: req.body, GET: req.query};
  req.customer = methods[req.method] || false;
  return next();
}

StackExchange Code Review Q#39568, answer score: 9